A plastic injection mold is a fully self contained tool. A MUD insert is a insert set that requires the use of a MUD frame to operate in an injection molding machine. Other than that, all the definitions that follow apply to both.

A two plate tool is a tool that has a female side (cavity side) and a male side (core side). It is the basic building block that all tools are made of.

A three plate tool is a tool with a stripper plate. The stripping action can take place on the cavity side as in a three plate runner or on the core side as a system of ejection.

When there is an action on both sides of the tool you technically have four plate tool.