Which of the following describes an acute angle?

An acute angle is defined as an angle that measures less than 90 degrees. This definition is fundamental in geometry. Angles are classified based on their measurements: a right angle is exactly 90 degrees, an obtuse angle measures more than 90 degrees but less than 180 degrees, and a reflex angle measures more than 180 degrees but less than 360 degrees.

Therefore, since acute angles are specifically characterized by their measurement being less than 90 degrees, the correct answer accurately encapsulates this definition. Recognizing the distinctions between the types of angles is essential for understanding their properties and relevance in various geometric contexts.