Spike Tetrahedron

A spike tetrahedron is a long, thin tetrahedron with two vertices close to one endpoint of its long direction, a third near an interior position, and a fourth near the opposite endpoint (Cheng et al. 2012, p. 25; Hannukainen et al. 2017, p. 3).

In the degenerate limit, the close pair coalesces and the four vertices approach three distinct positions on a line. A spear tetrahedron instead has the close pair near an interior position. These are qualitative names used in tetrahedral mesh classification.