**Definition:**The measure of an angle with a measure between 0° and 90° or with less than 90° radians is called an acute angle.

Also Known As: A positive angle that measures less than 90°

When the term is given to a triangle: Acute Triangle, it means that all angles in the triangle are less than 90°

Note: if the angle is 90°, it is then called a Right Angle. It is important to note that the angle must be less than 90° to be defined as an acute angle.