Rapid tooling is, simply, the creation of a mold in a shortened timeline.
Rapid tooling got its start in the 1990s, when engineers involved in injection molding wanted to see if they could build molds in a matter of hour or days instead of the weeks or months a machined mold would take. A rapid-tooled mold is ideal for prototyping a part and molding a few hundred plastic parts before full-scale, high-volume production starts.