Because it has 6 equal faces
A figure that has 6 rectangular faces is called a rectangular prism .
6
A cube has 6 faces and 8 corners.
A cube has 6 faces. The number of faces, alone, is not sufficient to figure out the number of edges. For example, a cube has 12 edges. A pentagonal pyramid also has 6 faces, but it has 10 edges.
Because it has 6 equal faces
A solid figure with eight vertices and all faces of equal size is called a cube. Each face of a cube is a square, and a cube has 8 vertices and 6 faces.
A figure that has 6 rectangular faces is called a rectangular prism .
A cube is a 3D shape that has 6 faces of equal area.
6
Cube
A triangular based pyramid would seem to fit the given description which has 4 equal sided triangular faces, 6 edges and 4 vertices.
square
a parallel piped figure has 6 faces
A cube has 6 faces and 8 corners.
Cube
a square pyramid