Concave. Indention or sunken area of a surface; the incuse surface in a model, pattern, mold, die, or a piece made from any of these. The contraposition of concavity is convexity: a concave area in a die or concave lettering or detail, for example, would produce a convex area or raised (convex) lettering or relief in a piece struck from that die.

Highly concave or dished models would create highly convex or domed pieces. If two such dished models were used to create a piece it would appear lenticular, like a lens (while it may be difficult to strike, such items are easily created by casting). If one dished and one domed model was used it would create a piece said to be concavo-convex. Two domed models would create a piece with two concave sides, called concavo-concave.