What characterizes an acute triangle?

An acute triangle is defined by the characteristics of its angles. Specifically, every angle in an acute triangle measures less than 90 degrees. This distinguishes acute triangles from other types of triangles, such as right triangles, which have one angle measuring exactly 90 degrees, and obtuse triangles, which have one angle measuring greater than 90 degrees.

The property of having all angles less than 90 degrees means that the triangle is entirely "sharper" in appearance compared to right or obtuse triangles. Additionally, while an acute triangle can have varying side lengths, the definition is strictly concerned with the measures of the angles within the triangle, making the choice that states all angles are less than 90 degrees the correct characterization of an acute triangle.