In geometry, a simplex (plural: "simplices" or "simplexes"), sometimes called "n-simplex" is the "n"-dimensional analogue figure of the triangle. A triangle is a 2-simplex. The 0-simplex is the point, the 1-simplex is the line segment (line connecting two points). The 3-simplex is the tetrahedron, and the 4-simplex is the pentachoron.