A triangular based pyramid would seem to fit the given description
Pyramid
A polygonal pyramid.
pyramid
pyramid
a polygonal prism or a polygond
The description given fits to that of a pyramid
It is a pyramid
A triangular prism.
Four triangular faces.
A Triangular Prism
Triangular based pyramid
Polygonal Prism Actually, it is a polygonal pyramid. A polygonal prism would have two polygonal faces.