How many sides does a triangle have?

A triangle has three sides, which is the defining characteristic of this geometric shape. In geometry, triangles are classified based on their side lengths and angles; however, regardless of the classification, all triangles consistently have three sides. This fundamental property is essential in many areas of mathematics and is foundational for understanding more complex shapes and concepts. The number of sides is crucial for distinguishing a triangle from other polygons, with four sides identifying a quadrilateral, five sides corresponding to a pentagon, and so forth. Thus, the clear identification of a triangle having three sides is what makes the choice correct.