An **angle** is formed when two lines meet at a point. That point where the two lines meet is called the **vertex**, while the two lines are called the sides of an angle, and **degree** is a measure of the angle. The higher the
degree, the more wide "open" the angle is. By definition, an angle that is 90 degrees is called a **right** angle, while an angle of 180 degrees is simply a straight line.

The word "geometry" is derived from the Greek words "geo" and "metri", which mean earth and measurement, respectively. Accordingly, then, geometry is concerned with questions of shape, size, relative position of figures, and the properties of space. Because angles are such an integral part of geometry, it is a good chance that you'll come across at least one question on the GRE math section where you'll need to apply your knowledge of the properties of angles.

As a first step, you should understand how angles are named. Angles can be designated in one of several ways:

- An angle can be designated by a letter
- An angle can be designated by using the vertex
- An angle can be designated by using the vertex and two points that lie on the sides of the angle

Below are several angles.