pyramid
It could be a pyramid.
A triangular pyramid is a three dimensional figure whose base is a triangle in shape. Triangular pyramids also have three side faces that are also triangles, four vertices, and six edges.
It is simply called a face.
A hemisphere is one example.
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.
A tetrahedron is a three-dimensional figure with four equilateral triangles. Every pyramid with a triangle as the base is a tetrahedron.
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.
A triangular pyramid is a three dimensional figure whose base is a triangle in shape. Triangular pyramids also have three side faces that are also triangles, four vertices, and six edges.
It can be a triangular based pyramid
It is simply called a face.
A hemisphere is one example.
Cone
There is no such thing as a 3-dimensional triangle. A triangle is a 2-dimensional figure. So, depending on what you mean exactly, the volume can vary. In the case of a pyramid - whether it has a triangular base, a rectangular base, or any other base - the volume is (1/3) Bh, that is, 1/3 times the area of the base times the perpendicular height.