In geometry, the ∠ (angle) symbol is used to denote an angle formed by three points. The middle point corresponds to the vertex at which the angle lies. Typically the angle symbol is used in an expression like this:
In plain language this means the angle is formed by the three points A, B, and C with the vertex at point B. For example, this expression could be used to reference the angle illustrated in the figure below.
An angle is defined as the amount of rotation between two rays. The point where the rays start is called the vertex.
The notation for a symbol is a small symbol written in text, sometimes followed by three letters that correspond to a figure.