An angle.

When two straight lines come together, they make an angle. The two lines are called the sides of the angle, and they meet at a point. A flat surface (called a plane) also forms an angle when it meets another.

To represent an angle, Greek letters such as \displaystyle{ \alpha } (alpha), \displaystyle{ \beta } (beta), \displaystyle{ \gamma } (gamma) and \displaystyle{ \theta } (theta) are sometimes used. An angle indicates the space between its sides, or the amount of rotation needed to make one side coincide the other.