Which geometric shape is defined as having three sides and three angles?

A geometric shape that is defined as having three sides and three angles is known as a triangle. This shape has distinct characteristics: each side connects two vertices, and the sum of the internal angles in a triangle always equals 180 degrees. Triangles can also be categorized based on their sides (such as equilateral, isosceles, and scalene) or their angles (such as acute, right, or obtuse).

In comparing this with the other options, a rectangle has four sides and four right angles; a circle is a shape with no sides and no angles, defined as the set of all points equidistant from a center point; and a pyramid typically has a polygonal base and multiple triangular faces converging at a single vertex, which does not conform to the definition of having only three sides and three angles. Therefore, the properties of a triangle align perfectly with the definition provided in the question.