A cap tetrahedron is a nearly flat tetrahedron with one polyhedron vertex close to the triangle interior of the opposite face. It is one of the qualitative shape types used in tetrahedral mesh classification (Cheng et al. 2012, p. 25; Hannukainen et al. 2017, p. 3).
In the degenerate limit, the four vertices lie in a plane, with one inside the triangle formed by the other three. A spade tetrahedron instead has a polyhedron vertex approaching the interior of an opposite polyhedron edge.
-Simplices." Appl. Math. 62,
1-13, 2017.