The GTP in "Pontiac GTP" stands for "Grand Touring Prototype." It is the street-legal version of endurance racing vehicles used in races like 24 Hours of Le Mans, the FIA World Endurance Championship and the Le Mans racing series.
Pontiac GTP vehicles were introduced in the early 1990s. They were designed as high-performance alternatives to standard GTs, with faster engines and the option to raise transmission shift points for more powerful acceleration. Many GTP vehicles also came with additional standard features such as OnStar and leather interiors. The GTP package remained available on Pontiac vehicles until 2006, when it was replaced by the GXP.