Geometry Glossary - Quick Reference

2d

This is an abbreviation of the term Two Dimensional. It is used to describe shapes drawn on a flat surface such as paper which have no volume.

3d

This is an abbreviation of the term Three Dimensional. It is used to describe shapes which take up space, ie they have volume.

Angle

The distance, measured in degree between two lines.

Apex

The highest point of a geometric shahpe.

Arc, circle

This is the length of the portion of circumference of the circle created between two radii.

Area

The amount of space contained within the perimeter of a shape.

Block/Box

The 3d form of a rectangle or square.

Circle

A closed curve where all points are an equal distance from the center point.

Circumference

A term given to the perimeter of a closed curve.

Cone

A 3d shape created by a circular base a triangles.

Congruent

Two shapes that are the same size and shape are congruent.

Cube

A three dimensional shape created by squares. It has six sides.

Cylinder

A 3d shape created by two equal sized circles and lines of equal length connecting them.

Diameter

This is the distance from one side of a circle to the other which also goes through the center point.

Formula

This is an equation written in the form of X = Y where X is the information you are looking for and Y is the standard calculation including variables required to achieve X. A formula can be difficult to establish, but once established this work does not have to be repeated every time the problem arises.

Hemisphere

Half a sphere.

Hexagon

A polygon with six sides and six vertices.

Oblique Cylinder

A cylinder that does not stand at a right angle from its base.

Oblique Prism

A prism that does not stand at a right angle from its base.

Octagon

A polygon with eight sides and eight vertices.

Parallel

Two or more lines that never touch through infinity.

Parallelogram

A four sided figure constructed with two sets of parallel lines.

Pentagon

Any five sided polygon.

Perimeter

The length of all sides of a polygon added together.

Perpendicular Height

This is the height of an object measured from its base to its highest point at an angle 90 degrees.

Pi

Pi is a constant in math. It is approximately 3.14159. It is the ratio between a circles circumference and diameter.

Polygon

A figure created by any number of straight lines meeting at any angle, that is closed.

Polyhedron

A three dimensional shape composed of flat faces with straight edges.

Prism

A three dimensional shape composed of two flat faces joined by sides that are perpendicular to them.

Pyramid

A three dimensional shape composed of a regular polygon (usually a square) with its face composed of congruent triangles joined at the apex of the pyramid.

Quadrilateral

A shape composed of four lines which is closed.

Radian

An alternative method of angle measurement. It is equal to 180/π

Radius

A line segment of a circle drawn from the center to its perimeter.

Radii

The plural form of radius.

Rectangle

A quadrilateral shape where opposite sides are equal in length, and all angles are 90 degrees (right angles).

Rhombus

A four sided polygon with all four sides equal in length.

Right Angle

90 degree angle.

Sector

A portion of a circle created by two radii and an arc.

Semicircle

A two dimensional shape that is half a circle. Because it is half a circle, the arc of a semi circle always measures 180 degrees.

Sphere

A three dimensional shape, where all points on the surface are an equal distance from the spheres center point (radii). The center point of a sphere is not part of the sphere.

Square

A polygon composed of four equal sides and angles.

Surface Area

Is the amount of an object you can see. A useful way to think of this, is to consider how much material is required to make the shape.

Trapezoid

A quadrilateral where two sides are parallel.

Triangle

A two dimensional shape composed of three lines of any length, joined at any angle.

Triangle (right angled)

A triangle, where two of the line join at 90 degrees.

Vertex

A point where two lines of a polygon meet.

Volume

How much space a three dimensional shape occupies. A good way to consider volume is to ask, how much water a 3d shape can hold.