It is simply called a face.
Tetrahedron
pyramid
It could be a pyramid.
Cone
A hemisphere is one example.
A pyramid.
Tetrahedron
A three dimensional triangular figure with three faces and a base is called a triangular pyramid. It has four vertices, four faces, and six edges.
Because the base of a cone is round, it is the only three dimensional figure with only one vertex.
pyramid
pyramid or cone
It could be a pyramid.
Cone
It can be a triangular based pyramid
A hemisphere is one example.
The line or plane upon which a geometric figure is thought of as resting is called the base. A three-dimensional figure with a circular base and the top meeting at a vertex; it resembles a funnel cone.
Tetrahedron has three sides and a base all triangular.