**Two angles that share a common side and a common vertex, but have no common interior points are called adjacent angles, often abbreviated as "adj."** Adjacent angles lie side by side to each other. Their shared common arm is also called a ray or an edge.

There are three types of adjacent angle pairs. Adjacent angles which add up to 90 degrees, or form a right angle together, are called complimentary angles. Adjacent angles which sum to 180 degrees, a straight line, are known as supplementary angles. Adjacent angles that form a complete angle, 360 degrees or one turn, are called conjugate or explementary angles.