An octagonal pyramid.
There is a contradiction in your question. If the base has four equal sides then is it a square so not all the faces are Triangles. However if the base is a square and the rest of the faces are triangles then your object is a "Square-based Pyramid"
The answer to your question, is an Octahedron.
An octagonal pyramid
No, the sides of the Great Pyramid of Giza are not equilateral triangles. The pyramid is a square-based pyramid, meaning it has a square base and four triangular faces that rise to a single apex. While the triangular faces are isosceles triangles with two equal sides, they are not equilateral, as the base of each triangle is not equal in length to the other two sides.
A pyramid with a triangular base. The faces are 4 equilateral triangles.
square pyramid
There is a contradiction in your question. If the base has four equal sides then is it a square so not all the faces are Triangles. However if the base is a square and the rest of the faces are triangles then your object is a "Square-based Pyramid"
an octagon
The answer is a pyramid.
octagonal pyramid :)
The answer to your question, is an Octahedron.
An octagonal pyramid
A pyramid.
A regular octagonal pyramid.
The figure is a pyramid and the base is a square.
This object is called an octahedron
Pyramid - square pyramid to be exact.