In the broadest sense, rapid tooling is any method or technology that enables you to produce tooling quickly. Many business agree, however, that it means tooling driven by an additive manufacturing (AM) process is the key to making it rapid.
DirectSteel injection mold and molded parts, courtesy of EOS
Two categories of rapid tooling have developed. One is an indirect approach that uses one or more master patterns to produce a tool. An example is epoxy-based composite tooling.
The second category is a direct approach, meaning that an AM process builds the core and cavity mold inserts directly, in the case of injection mold tooling. Direct metal laser sintering from EOS has been used to produce these types of tools.