In the world of car racing, there had been rules set by various racing organizations to try and even the odds for racing teams with differing budgets. One of the ways you could do this is by forcing all teams to use cars that were commercially available.
This led to the production of cars in order to adhere to the letter of the rules. A company would design a car for racing, and make a certain amount (set by the race organizations) commercially available in order to satisfy the rules. This would theoretically allow Joe Shmoe's race team to buy the same Mitsubishi Lancer Evolution VI that the factory-sponsored Mitsubishi team would be racing.
The cool upshot of these rules is that they force car companies to make some kick-ass cars that are commercially available. Unfortunately, homologation rules are becoming a thing of the past.