To the very tiny dot left by a very sharp pencil is given the name of point.

To the very fine trace made by a very sharp pencil is given the name of line.

A very thin sheet of tissue paper gives us the idea of surface.

To all things that occupy space is given the name of solid.

The straight line is unlimited, direct, and does not change direction throughout its length.

A curved line changes its direction continually from point to point.

A broken line is made up of line segments not going in the same direction, connected so that successive segments have an end point in common.

A ray is each of the two portions obtained by dividing a straight line by a point.

A line segment is that part of the straight line which is limited by two points.

The point which divides the straight line into two equal parts is given the name of origin of each ray.

The end points are the two points that limit a line segment.

A straight line is called horizontal when it follows the direction of still water.

A straight line is called vertical when it follows the direction of a plumb line.

A straight line is called oblique when it follows neither the direction of still water nor the direction of a plumb line.

Two line segments are consecutive when they have only one extremity in common and do not lie on the same straight line.

Two line segments are adjacent when they have one extremity in common and lie on the same straight line.

Two straight lines are called parallel when lying on the same plane, as far as they go, they never meet, no matter how far they extend.

Two straight lines are called divergent when they go away from each other and therefore the distance between them increases.

Two straight lines are called convergent when they approach each other and therefore the distance between them decreases.

Two straight lines are called intersecting when the angles formed by them are not all equal.

Two straight lines are called perpendicular when crossing each other, they form four right angles.

The perpendicular straight line drawn through the midpoint of a line segment is given the name axis of the line segment.

An angle is each part of a plane limited by two rays having a common origin.

When the ray, after wheeling a complete turn, is superimposed to the ray, it forms an angle called a whole angle.

When two rays forming an angle are a prolongation of each other, they form a straight angle.

The angle which is half of the straight angle is called a right angle.

When an angle measures less than a right angle, it is called an acute angle.

When an angle measures more than a right angle, it is called an obtuse angle.

An angle which is greater than a straight angle, but less than a whole angle, is said to be a reflex angle.

The vertex of an angle is the common point from which the two rays forming an angle originate.

The sides of an angle are the two rays that form an angle.

The measurement of an angle is given the name size and is expressed in degree.

When an angle does not contain the extensions of its sides, it is called a convex angle.

When an angle contains the extensions of its sides, it is called a concave angle.

Angles having the vertex and one side in common are called adjacent angles.

The opposite non-adjacent angles formed by two intersecting straight lines are called vertical angles or opposite angles. SHAPE \* MERGEFORMAT

Two angles whose sum is equal to a right angle, and therefore to 90(, are called complementary angles.

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Two angles whose sum is equal to a straight angle, and therefore to 180(, are called supplementary angles.

The angles formed on the inner side of two straight lines cut by a transversal are called interior angles.

The angles formed on the outer side of two straight lines cut by a transversal are called exterior angles.

Interior angles lying diagonally on opposite sides of the transversal are called alternate interior angles.

Exterior angles lying diagonally on opposite sides of the transversal are called alternate exterior angles.

Interior angles lying on the same side of the transversal are called interior angles on the same side of the transversal.

Exterior angles lying on the same side of the transversal are called exterior angles on the same side of the transversal.

Two angles, one exterior and one interior, each on one of the two straight lines, and lying on the same side of the transversal, are called corresponding angles.

A ray that divides an angle into two equal parts is called a bisector.

Any figure bounded by a broken straight line is called a polygon.

A plane figure bounded by a closed curve line is called a simple closed curve.

A polygon bounded by three line segments is called a triangle.

A polygon bounded by four line segments is called a quadrilateral or a quadrangle.

All the polygons bounded by more than four line segments retain the general name of polygons, but each takes its particular name according to the number of its line segments.

The plane figure limited by a closed curve having all the points equidistant from a fixed point is given the name circle.

The plane figure similar to an oval having the two minor arcs equal is given the name ellipse.

The plane figure similar to an egg is given the name oval.

The triangle with all its sides equal is called an equilateral triangle.

The triangle with two sides equal is called an isosceles triangle.

The triangle with all its sides unequal is called a scalene triangle.

The triangle that has one right angle is called a right-angled triangle.

The triangle that has one obtuse angle is called an obtuse-angled triangle.

The triangle that has three acute angles is called an acute-angled triangle.

The part of the plane limited by the sides of a triangle is called its surface.

The line segments which enclose a triangle are called its sides.

The side opposite each vertex may be considered a base of the triangle.

The total of the sides of a triangle is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a triangle is an angle.

The point where two sides of a triangle meet is a vertex (plural: vertices).

A line segment from any vertex of a triangle, drawn perpendicular to its opposite side is called an altitude of the triangle.

A line which bisects one angle and extends to the opposite side is called a bisector of the triangle.

Every line segment joining a vertex to the mid-point of the opposite side is called a median.

A straight line extending from the mid-point of a side, perpendicular to that side, to the opposite side is called an axis.

In a right-angled triangle the side opposite the right angle is called the hypotenuse.

In a right-angled triangle the sides forming the right angle are called the legs (or catheti) of the triangle.

When the legs of a right-angled triangle are equal, it is called a right-angled isosceles triangle.

When the legs of a right-angled triangle are unequal, it is called a right-angled scalene triangle.

A quadrilateral with no parallel sides is called a common quadrilateral or a trapezium.

A quadrilateral which has only one set of opposite sides parallel is called a trapezoid.

Any quadrilateral whose opposite sides are parallel is called a parallelogram.

Any parallelogram containing four right angles is called a rectangle.

Any parallelogram having four equal sides is called rhombus.

A parallelogram having four right angles and four equal sides is called a square.

The part of the plane enclosed inside a parallelogram is called its surface.

The line segments which bound a parallelogram are called its sides.

Any side of a parallelogram can be called its base. The base usually refers to the side on which the parallelogram rests.

The total of the sides of a parallelogram is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a parallelogram is called an angle.

A point where two sides of a parallelogram meet is called a vertex (plural: vertices).

The perpendicular distance between two opposite side is called the altitude.

Each line segment which joins opposite vertices of a parallelogram is called a diagonal.

The part of the plane enclosed inside a rectangle is called its surface.

The line segments which bound a rectangle are called its sides.

Any side of a rectangle can be called its base. The base usually refers to the side on which the rectangle rests.

The total of the sides of a rectangle is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a rectangle is called an angle.

A point where two sides of a rectangle meet is called a vertex (plural: vertices).

The perpendicular distance between two opposite side is called the altitude.

Each line segment which joins opposite vertices of a rectangle is called a diagonal.

The part of the plane enclosed inside a rhombus is called its surface.

The line segments which bound a rhombus are called its sides.

Any side of a rhombus can be called its base. The base usually refers to the side on which the rhombus rests.

The total of the sides of a rhombus is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a rhombus is called an angle.

A point where two sides of a rhombus meet is called a vertex (plural: vertices).

The perpendicular distance between two opposite side is called the altitude.

Each line segment which joins opposite vertices of a rhombus is called a diagonal. The longer diagonal is the major diagonal, and the smaller is the minor diagonal.

The part of the plane enclosed inside a square is called its surface.

The line segments which bound a square are called its sides.

Any side of a square can be called its base. The base usually refers to the side on which the square rests.

The total of the sides of a square is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a square is called an angle.

A point where two sides of a square meet is called a vertex (plural: vertices).

The perpendicular distance between two opposite side is called the altitude.

Each line segment which joins opposite vertices of a square is called a diagonal.

The part of the plane enclosed inside a trapezoid is called its surface.

The line segments which bound a trapezoid are called its sides.

The longer of the parallel sides is called the major base.

The shorter of the parallel sides is called the minor base.

The total of the sides of a trapezoid is called its perimeter.

Each part of the plane enclosed between two consecutive sides of a trapezoid is called an angle.

A point where two sides of a trapezoid meet is called a vertex (plural: vertices).

The perpendicular distance between two opposite side is called the altitude.

Each line segment which joins opposite vertices of a trapezoid is called a diagonal.

A trapezoid whose non-parallel sides are equal is called an isosceles trapezoid.

A trapezoid which has two non-parallel sides of unequal length is called a scalene trapezoid.

A trapezoid having one of its non-parallel sides perpendicular to its base is called a right-angled trapezoid.

A polygon having unequal sides and angles is called an irregular polygon.

A polygon with equal angles but unequal sides is called an irregular polygon.

A polygon with equal sides but unequal angles is called an irregular polygon.

A polygon having equal angles and equal sides is called a regular polygon.

A point where two sides of a polygon meet is called a vertex (plural: vertices).

A line segment drawn from one vertex to another vertex which is not consecutive is called a diagonal.

The point which is equidistant from all vertices and from all the sides is called the center of the polygon.

The line segment drawn from the center of a polygon to one of the vertices is called the radius of the polygon.

The perpendicular line segment drawn from the center of a polygon to the mid-point of one of the sides is called the apothem.

The part of the plane within the outline of the circle is called the surface.

The fixed point within the circle from which all points of the closed curve are equidistant is called the center.

The closed curve made up of points equidistant from the center is called the circumference of the circle.

A line segment joining the center to any point of the circumference is called the radius (plural: radii).

A line segment joining any two points on circumference is called a chord.

A line segment passing from one point on the circumference, through the center, to another point on the circumference is called the diameter.

A part of the circumference limited by two points is called an arc.

Each of the two equal parts obtained by dividing the circumference along the diameter is called the semi-circumference.

Each part of a circle formed by a semi-circumference is called semi-circle.

The figure formed by two radii and the intercepted arc is called a sector of the circle.

The figure formed by a chord and its arc is called a segment of the circle.

The straight line having no point in common with the circumference is external to the circle.

A straight line which intersects the circumference at two points is secant to the circle.

Two circles which have no point in common, one outside the other, are called external.

Two circles which have no point in common, one inside the other, are called internal.

Two circles having only one point in common and internal to each other are called internally tangent.

Two circles having only one point in common and external to each other are called externally tangent.

Two circles having two points in common are called secant.

Circles having the same center are called concentric.

The part of the plane enclosed between two concentric circles is called the annulus.