Sides $($or$)$ Arms of an angle

The lines which form angle an angle by their intersection at a point are called the sides of an angle. They are also called as arms of an angle.

Example

$\overrightarrow{PQ}$ and $\overrightarrow{PR}$ are two lines and they both have a common $P$ where an angle is made.

The lines $\overrightarrow{PQ}$ and $\overrightarrow{PR}$ are reason for the forming an angle. So, the lines $\overrightarrow{PQ}$ and $\overrightarrow{PR}$ are called the sides of an angle and they are called a arms of an angle.