Right Angle 

Right Angles is the plural of Right Angle.

A Right Angel is an angle that has a measure of 90 Degrees. 

A Square contains four Right Angles.

The construction tool called a Square can be used to measure Right Angles.

An object makes a Right Angle with another object when it points 90 Degrees from the direction the other object is pointing.  It it sometimes said the the second object is Square Therewith the first object.