A prism??? O.o sounds like it to me anyway...
A pentagonal prism
A triangular prism. :)
A pyramid with a triangular base. The faces are 4 equilateral triangles.
A triangular prism would fit the given description
Triangular prisim. The three faces are rectangles, while the two bases are triangles.
A triangular-based pyramid - it consists of four equilateral triangles, joined at the points.
There are several: a tetrahedron with 4 equilateral triangles. An 8-sided solid (think of 2 Egyptian pyramids, turn one upside down and put the two square bases together). A 20-sided also has equilateral triangles.
It is a tetrahedron pyramid
It is a regular octahedron.