What is a 3D shape that has two identical ends and all flat sides referred to as?

A 3D shape that has two identical ends and all flat sides is known as a prism. This geometric figure is characterized by its uniform cross-section along the length of the shape, with both bases being congruent polygons. For example, if the bases are triangles, the prism is a triangular prism; if they are rectangles, it's a rectangular prism, and so on.

Prisms can take on many forms depending on the shape of the bases, but they all share this essential property of having two identical parallel faces (the bases) and flat lateral faces that connect these bases. This geometric configuration is what distinctly classifies it as a prism.

The other choices represent different shapes: a pyramid has a single base and triangular faces that converge at a point; a sphere is a perfectly round shape with no edges or vertices; and a cube, while having flat sides, has all faces square and is not defined by the property of having two identical ends. Thus, the defining features of a prism clearly align with the question's description.