Which characteristic best describes an obtuse triangle?

An obtuse triangle is specifically defined by having one angle that measures more than 90 degrees. This characteristic is fundamental to the classification of triangles based on their angles. In contrast, a triangle where all angles are less than 90 degrees is known as an acute triangle, and a triangle with one right angle is classified as a right triangle. The option mentioning equal side lengths refers to an equilateral triangle, which has all sides and angles equal, thus not applicable to obtuse triangles. Therefore, option B accurately captures the defining characteristic of an obtuse triangle, distinguishing it from other types of triangles based on the measure of its internal angles.