Which triangle has all angles measuring less than 90 degrees?

A triangle with all angles measuring less than 90 degrees is classified as an acute triangle. In such triangles, each of the three interior angles is acute, meaning that they each measure greater than 0 degrees but less than 90 degrees. This characteristic is what defines the acute triangle distinctively from other types of triangles.

In contrast, an obtuse triangle includes one angle that is greater than 90 degrees, thus disqualifying it from being acute. A right triangle, by definition, contains one right angle that measures exactly 90 degrees. A scalene triangle refers to the lengths of its sides rather than the measure of its angles; while it can be acute if all angles are less than 90 degrees, it does not specify that characteristic outright. Therefore, the defining feature of an acute triangle is that all its angles are less than 90 degrees, making it the correct choice for this question.