Plates, which contain the part-cavity in the injection mold are called mold plates.
Usually there is one mold plate for the injection side and one for the ejection side.
Dependent on the complexity of the part, the cavity is carved directly into the mold plate or embeded with inserts into the mold plate.
The primary cooling system of the cavity is located in the mold plates as well.
This glossary of plastic industry is provided by PLEXPERT Canada Inc.