What do you call an angle that has a degree measure of exactly 180 degrees?

An angle that measures exactly 180 degrees is known as a straight angle. This type of angle forms a straight line when the sides of the angle are extended. Visually, it represents a half-turn, clearly illustrating that the two rays are aligned in opposite directions.

Understanding the distinction between angles is essential. For example, a reflex angle is one that measures more than 180 degrees but less than 360 degrees, meaning it exceeds the straight angle. Complementary angles are those that sum up to 90 degrees, and supplementary angles refer to two angles that together total 180 degrees, but by definition, only one of those angles can be a straight angle on its own. Therefore, the specificity of a straight angle being exactly 180 degrees makes it a unique and defined entity in geometry.