A square is not a solid figure at all. It's a flat figure, with four congruent faces and four congruent angles.
A square pyramid.
A triangular prism. :)
The only thing I can come up with would be a tetrahedron. You could make a pyramid with a square (open) base, I guess.
The figure is a pyramid and the base is a square.
the solid figure with six congruent sides isva cube