Geometry Vocabulary

Terms

Description

Point

Point is a location represented by a dot or a position in space.

Line

A one-dimensional figure, which has length but no width.

Line Segment

Segment (part) of a line.

Ray

In geometry, the ray is a part of a line that has a fixed starting point but no endpoint.

However, it can extend infinitely in one direction.

Besides this, on its way to infinity, a ray may pass through more than one point.

Intersecting line segments

For lines, rays, and line segments, the word intersect means to meet or cross. When two lines, rays, or line segments meet at a point, we call it an intersecting point.

Parallel line segments

When the two line segments do not cross each other, in other words they do not intersect (never meet) we call these segments as parallel line segments.

Perpendicular line segments

When two line segments stand in a way that they make a ‘T’ shape, such a type of arrangement is called perpendicular line segments.

So, here one line segment is perpendicular or at right-angle or 90-degrees to another line segment.

Square

A square is formed by four line segments of equal length each, which means that the square has all four sides equal.

Rectangle

A rectangle is a 2-D shape having four sides and four corners.

Its two sides meet at right angles or 90-degrees, which means a rectangle has 4 angles, each measuring 90 ̊.

Also, the opposite sides of a rectangle have the same lengths and are parallel.

For example, unlike a square, two line segments are of say ‘20 m’ and the other two line segments are of ‘8 m’. So when joined, they form a rectangle.

Triangle

A triangle is a polygon with three edges or sides (whose measure can/cannot be equal) and three vertices.

These three line segments can be of equal length.

Two segments can be of the same length, and the other different.

It is also possible that all three line segments are of different lengths.

Equilateral Triangle

A triangle having all its sides equal is an equilateral triangle.

Isosceles Triangle

A triangle that has two sides of equal length while the third one is of a different length, we call this triangle an isosceles triangle.

However, when a triangle has an angle of 90-degrees between two sides, it is a right-angled isosceles triangle.

Scalene Triangle

When all sides of a triangle are of different lengths, we call it a scalene triangle.

Vertices (Singular: Vertex)

A point where two or more line segments meet is called a vertex. And its plural form is vertices.

Circle

A 2-D shape that has no edge or side or a vertex.

Though a circle doesn’t have any side, it has a circumference, diameter, and radius, which is denoted by ‘r’.

Circumference

The length of the line enclosing a circle is called its circumference.

Radius

Radius is defined as half of the diameter of a circle.

The length of the line so formed is a diameter. When we half this length, it becomes the radius of a circle.

Quadrilateral

The word ‘Quad’ means four.

Any polygon having four sides is a quadrilateral.

Rhombus

Rhombus is a quadrilateral whose four sides have the same length.

Angles

An angle is the space between two lines or surfaces that meet, measured in degrees.

These angles can be right, acute, and obtuse.

Linear or 180-degree angle

Look at your forehead and measure the angle, you notice that the angle is 180-degrees.

Right Angle

An angle that forms between two lines forming a T-shape is called a right-angle.

Acute Angle

Suppose that you have a T-shape made of two lines and let us tilt one line, you see that there is a change in the angle and that is less than 90-degrees.

Thus, the angle formed here is an acute angle.

Obtuse Angle

When an angle is between 90 and 180-degrees, it is an obtuse angle.

For example, if you tilt the ‘T-shape’ in such a way that the angle lies between 90-180, this shape has an obtuse angle.