A spear tetrahedron is a long, thin tetrahedron with two nearby vertices close to an interior position along its long direction and the other two near opposite ends (Cheng et al. 2012, p. 25; Hannukainen et al. 2017, p. 3).
In the degenerate limit, the close pair coalesces at an interior point of the line segment joining the other two vertices. It need not be the midpoint. A spike tetrahedron instead has its close pair near an end. These names describe qualitative shape types in tetrahedral mesh classification.
-Simplices." Appl. Math. 62,
1-13, 2017.