Basic terms
Types of angles
Angle relationships
Points, points, points
Lines, lines, lines
100

This is the building block of everything in Geometry. It is a "dot" in space, often labeled with a single letter of the alphabet.

What is a point?

100

This angle is greater than 0 degrees, but less than 90 degrees.

What is an acute angle?

100

This is a word that describes angles or shapes that are exactly the same size & shape.

What is congruent?

100

This is what we call the point where two lines cross.

What is an intersection?

100

Two lines that move in the same direction but never cross.

What are parallel lines?

200

This connects two points, which act like endpoints. It does not go on forever in either direction.

What is a segment?

200

This angle is 90 degrees exactly.

What is a right angle?

200

This a word that describes angles that touch each other (share a ray as a side), but do not overlap at all.

What is adjacent angles?

200

This is the point where two rays originate from, creating an angle. It is also a corner for any polygon.

What is a vertex?

200

These are lines that cross each other at a perfect 90 degree angle.

What are perpendicular lines?

300

This connects two points but continues all the way through them, going on towards infinity in both directions.

What is a line?

300

This angle is greater than 90 degrees but less than 180 degrees.

What is an obtuse angle?

300

This word describes angles that add up to 180 degrees.

What is supplementary?

300
This is a word to describe three or more points that fall on the same line.

What is collinear?

300

When two lines cross each other, the angles directly across from each other are equal in measure and are called this.

What are vertical angles?

400

This originates from a single endpoint, and moves in one direction through a second point. It passes through the second point, traveling forever.

What is a ray?

400

This an angle that is 180 degrees exactly.

What is a straight angle?

400

This word describes angles that add up to 90 degrees.

What is complementary?

400

This is the name for four or more points that fall on the same plane.

What is coplanar?

400

If a line cuts a segment or angle perfectly in half, we give it this special name.

What is a bisector?

500

This is a two-dimensional flat surface that extends without end. It is made up of many points and has no thickness.

What is a plane?

500

This is angle greater than 180 degrees, but less than 360 degrees.

What is a reflex angle?

500

This tool can be used to measure angles.

What is a protractor?

500

This is what we call the point where an x and y axis cross each other in a coordinate plane.

What is the origin?

500

The name we give a line that cuts a segment perfectly in half at a perfect 90 degree angle.

What is a perpendicular bisector?