In geometry, a truncation is an operation in any dimension that cuts polytope vertices, creating a new facet in place of each vertex. The diagram below shows a 50% truncation of a dodecahedron, the dissection point is 50% of the edge length from a vertex then the face is sliced away. This is then repeated with all of the dodecahedron vertices to produce an Icosidodecahedron.

Less than 50% truncation will produce smaller triangle facets more than 50% will produce smaller pentagons 100% truncation will produce the dual (an Icosahedron)