A polyhedron with four triangular faces. In a regular tetrahedron all four triangles are congruent equilateral triangles. It constitutes a regular triangular pyramid.
Mathematics
A solid figure bounded by four triangular faces, with four vertices and six edges. A regular tetrahedron has equilateral triangles as its faces, and so all its edges have the same length.
Chemistry
A polyhedron with four triangular faces. In a regular tetrahedron all four triangles are congruent equilateral triangles. It constitutes a regular triangular pyramid.
Geology and Earth Sciences
A four-faced crystal form in which each face is an equilateral triangle. It may be referred to three equal crystallographic axes at right angles which join the centres of opposite edges of the crystal. It is a special form within the cubic system with the symbol (111).