Which of the following describes an acute angle?

An acute angle is defined as an angle that measures greater than 0° and less than 90°. This means it occupies a position in the first quadrant of a circular plane, where it appears narrow and sharp in appearance. Recognizing acute angles is fundamental in geometry as they are used in various applications, including trigonometry, where they are essential for calculations involving sine, cosine, and tangent.

The other descriptions do not fit the definition of an acute angle: an angle greater than 90° is classified as obtuse, an angle less than 0° does not exist in the standard angular measurement, and an angle equal to 180° is defined as a straight angle. Therefore, the choice that accurately describes an acute angle is the one that specifies the angle's measurement range.