Stock, in this case, means not stock at all. For example, use of $10,000 aftermarket shocks and $2,000 race tires is not only encouraged, but required to be competitive in stock class competition.

Street prepared classes are where you spend a whole lot of money on your car to make it marginally faster and less competitive than it was in stock class.

The primary attraction of autocross is that it is a relatively inexpensive way to meet teenage girls brought to the races by their pimply faced, baseball-hat-on-backwards, Honda CRX driving boyfriends. Many clubs use this aspect of the sport to try to attract new members by featuring condom giveaways for novice drivers.