Parting line

Parting line or outsole parting-plane
The line in an outsole mold is made by the closing edges of the tooling. The tooling is split at the parting line. A mold may have one or 2 parting planes.  Extra rubber may spread out of the parting line, this will be need to be trimmed off.   A narrow tight parting line or parting plane  is a sign of quality tooling.