In the given figure, the ray will be named as:

A ray is a portion of a line. It starts at one point and goes endlessly on the other side.

While writing the name of a ray we always write the point from which the ray is starting at first and then the point to which the ray is directed. 

Here, the ray is starting from O and is directed towards A. 

Therefore, the ray will be denoted by $\overrightarrow{\mathrm{OA}}$ .