Plato associated the tetrahedron with fire, because the heat of fire feels sharp and stabbing like the tetrahedron.
The tetrahedron is a platonic solid consists of 4 congruent triangles.
It has 6 edges and 4 vertices. At each vertex 3 faces meet.
This is the simplest and smallest of the platonic solids. It is a kind of pyramid
The tetrahedron has 2 possible nets:
To view the 3D version:
https://www.mathsisfun.com/definitions/tetrahedron.html
How to make the net: