In geometry

Geometry

Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....

, adjacent angles, often shortened as adj. ∠s, are angle

Angle

In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

s that have a common ray coming out of the vertex going between two other rays. In other words, they are angles that are side by side, or adjacent.
A pair of angles is omplementary angles| if the sum of their measures is 90°.

A pair of angles is supplementary

Supplementary angles

Supplementary angles are pairs of angles that add up to 180 degrees. Thus the supplement of an angle of x degrees is an angle of degrees....

if the sum of their measures is 180°.
An angle with a ray connected to a common point down the center.