Which of the following best describes a straight angle?

In geometry, angles are classified based on their degree measurements:
* An acute angle is less than $90^{\circ }$.
* A right angle is exactly $90^{\circ }$.
* An obtuse angle is between $90^{\circ }$ and $180^{\circ }$.
* A straight angle is exactly equal to $180^{\circ }$, forming a flat straight line.

Thus, $180^{\circ }$ perfectly describes a straight angle.