This is a "trigonal pyramid" or "tetrahedron."
A three sided pyramid.
No such thing A tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. Similar to a pyramid but with a triangular base.
A triangular dipyramid - two triangular pyramids stuck together, base-to-base.
A regular polyhedron has equal size faces as in the case of a tetrahedron which is a triangular base pyramid that has 4 equilateral triangle faces.
Tetrahedron - a pyramid with a triangular base.
A square based pyramid.
A tetrahedron is a polyhedron with four triangular faces, while a triangular prism is a polyhedron with two triangular faces and three rectangular faces. The main difference between the two shapes is their number of faces and their base shapes. Additionally, a tetrahedron has four vertices and six edges, while a triangular prism has six vertices and nine edges.
hexagon base prism
A TETRAHEDRON, which is commonly referred to a a triangular based pyramid. The jokingly, a sphere. It has two faces, and outside face and an inside face, Ha!!!Ha!!!
There are a number of possible 7-sided polyhedra. Three that come immediately to mind are: a hexagonal pyramid, a pentagonal prism, a "stretched" triangular pyramid (triangular base, rectangular sides, and then triangular faces meeting at an apex).
This 3D shape could be a square based pyramid.
A tetrahedron.