A tetra is a three-dimensional geometric shape that has four triangular faces, six edges, and four vertices. It is one of the simplest forms of a polyhedron and is classified as a tetrahedron. The most common type of tetrahedron is the regular tetrahedron, where all faces are equilateral triangles, and all edges are of equal length. Tetrahedra can be found in various fields, including chemistry, where they represent the molecular geometry of certain compounds, such as methane. In mathematics, they are studied in topology and geometry for their unique properties and relationships with other shapes.