What does "truncated" mean?

Truncated: (Min.) Replaced, or cut off, by a plane, especially when equally inclined to the adjoining faces; as, a truncated edge.

Additional senses

  1. 2.(Zoöl.) Lacking the apex; -- said of certain spiral shells in which the apex naturally drops off. Truncated cone or pyramid (Geom.), a cone or pyramid whose vertex is cut off by a plane, the plane being usually parallel to the base.

Sources