# Overview of Geometry Terms

## 84 terms

### triangle

A polygon with three sides.

### square

A quadrilateral with four congruent sides and four right angles.

### perimeter

Sum of the lengths of all the sides.

### kite

A quadrilateral that has two pairs of adjacent sides that are the same length.

### diagonal

A line segment connecting any two nonadjacent vertices of a polygon.

### convex

Every line segment connecting interior points that is entirely contained with the figure's interior.

### parallelogram

A quadrilateral that has two pairs of opposite sides that are parallel.

### rectangle

A quadrilateral with four right angles.

### trapezoid

A quadrilateral that has only one pair of opposite sides that are parallel.

### equilateral triangle

A triangle with three congruent sides.

### polygon

A closed plane figure for which all sides are line segments.

### scalene triangle

A triangle with all three sides of different lengths.

### concave

A shape or solid which has a "cave" in it.

### congruent

Shapes that has the same size.

### isosceles triangle

A triangle with two congruent sides.

### regular polygon

A polygon whose sides and angles are congruent.

### n-gon

A polygon with n sides.

### dodecagon

A polygon with 12 sides.

### decagon

A polygon with 10 sides.

### consecutive sides

Two sides that are adjacent and one after the other.

A four-sided polygon.

### rhombus

A parallelogram with 4 congruent sides.

### hexagon

A polygon with 6 sides.

### pentagon

A polygon with 5 sides.

### octagon

A polygon with 8 sides.

### consecutive angles

Two angles that are adjacent and one after the other.

### septagon

A polygon with 7 sides.

### nonagon

A polygon with 9 sides.

### vertex

The point where both rays (sides) of an angle meet.

### equilateral triangle

A triangle in which all sides are the same length and all angles are the same size.

### right triangle

A triangle that has a right angle. (90 degree angle)

### obtuse triangle

A triangle in which one angle is larger than 90 degrees.

### acute triangle

A triangle in which all three angles are less than 90 degrees.

### isosceles triangle

A triangle in which two sides are the same length and the two base angles have the same measure.

### scalene triangle

A triangle in which no two sides are of the same length.

### hypotenuse

The longest side of a right triangle, opposite the right angle.

### leg (right triangle)

The two sides of a right triangle that form the right angle.

### base

The third side of an isosceles triangle, it may not be congruent to the other two sides.

### leg (isosceles triangle)

The two sides of an isosceles triangle that are congruent.

### equiangular triangle

A triangle in which the three angles are congruent.

Sides of a triangle that share a vertex.

### opposite side

The side across from an angle.

### triangle

A polygon with three sides.

### vertex angle

The angle opposite the base of an isosceles triangle.

### 180 degrees

The sum of the interior angles of a triangle.

### base angles

The angles opposite the congruent sides of an isosceles triangle.

### congruent triangles

Two triangles that are have the same shape and size.

### acute angle

An angle that measures less than 90 degrees.

### right angle

An angle that measures 90 degrees.

### obtuse angle

An angle that measures more than 90 degrees but less than 180 degrees.

### straight angle

An angle that measures exactly 180 degrees.

### complementary angles

Two angles whose sum of measures is 90 degrees.

### supplementary angles

Two angles whose sum of measures is 180 degrees.

### vertical angles

A pair of opposite angles formed by two intersecting lines. They are congruent.

Angles that share a common side and a common vertex.

### zero angle

An angle that measures exactly 0 degrees.

### vertex

The common endpoint of the two rays that make up an angle.

### congruent angles

Angles that have the same measure.

### angle

Two rays with a common end point.

### sides

The rays that make up an angle.

### degree

The unit used to measure angles in geometry (based on 360).

### protractor

An instrument used to measure angles.

### angle bisector

A ray that divides an angle into two congruent angles.

### point

It marks a location and is named by a capital letter; it has no thickness and 0 dimension.

### line

An infinite set of points that goes on forever; it has no thickness and it is one dimensional.

### plane

A flat surface that goes on forever in two directions; an infinite set of points; it has no thickness and is two dimensional.

### space

The set of all points. It is three dimensional.

### collinear

Points that lie on the same line.

### noncollinear

Points that do not lie on the same line.

### coplanar

Points that lie on the same plane.

### noncoplanar

Points that do not lie on the same plane.

### intersection

The set of points both figures have in common.

### segment

Part of a line consisting of two end points and all the points between them.

### ray

Part of a line that starts at a particular point and extends infinitely in one direction.

### perpendicular

Two lines that intersect to form right angles.

### parallel

Lines that do not intersect but are in the same plane.

### skew

Lines that are not parallel and do not intersect.

### opposite rays

Two rays that share a common endpoint but extends in opposite directions and makes a line.

### congruent segments

Segments that have the same length.

### midpoint

A point that divides a segment into two congruent segments.

### endpoint

Marks the end of a line segment or ray.

### segment bisector

A line that divides a segment at its midpoint to form two congruent segments.

### perpendicular bisector

A line that passes through the midpoint of a segment and is perpendicular to that segment.

### intersecting lines

Two lines that cross at a given point.