What is the definition of adjacent angles?

Adjacent angles are defined as two angles that share a common vertex and a common side but do not overlap, meaning they have no common interior points. This definition is essential in understanding the spatial relationship between angles in geometry. When two angles are adjacent, they can be visualized as sitting next to each other, separated only by the common side they share. This characteristic is crucial not only for solving geometry problems but also for understanding more complex relationships involving angles, such as in polygons.

The other options illustrate concepts that relate to angles but do not accurately describe adjacent angles. For example, complementary angles refer to pairs of angles that sum to 90 degrees, while angles that add up to 180 degrees are known as supplementary angles. Equal angles refer to angles that measure the same amount, which does not necessarily imply a relationship of adjacency. Hence, the correct definition highlights the specific criteria that classify angles as adjacent.