In geometry, the term adjacent is usually used to describe two angles or two sides of a polygon that are next to each other.
For example, in the rectangle above, side AB and side BD are adjacent sides because they are right next to each other.
Notice that side AB and side BD share a common vertex (vertex B)
In the figure below, angle ABD and angle DBC are adjacent angles because they are right next to each other.
Notice that angle ABD and angle DBC share a common vertex and a common side, but they do not overlap.