Undercard

In sports, a card comprises a listing of the matches taking place in a title match combat-sport event. Organizers divide overall cards into a main event match and the undercard, which encompasses the rest of the matches. One can also further subdivide the undercard into midcard and lower card, according to the perceived importance of the matches. Promoters schedule matches to occur in ascending order of importance.

The undercard, or preliminary matches (sometimes preliminary card), consists of preliminary bouts that occur before the headline or "main event" of a particular boxing,professional wrestling, horse racing, auto racing, or other sports event. (In auto racing, however, the term "support race" occurs more commonly.) Typically, promoters intend the undercard to provide fans with an opportunity to see up-and-coming fighters or fighters not so well known and popular as their counterparts in the main event. The undercard also ensures that if the main event ends quickly fans will still feel that they received sufficient value for the price of their admission.

In auto racing, support races occur not just before the feature race, they occur on qualifying day where attendances are typically low and after the completion of the feature race, purposely to lessen the effect of traffic congestion outside venues common in major championship rounds, as spectators make their way home. Examples of notable support races include Porsche Supercup and GP2 Series, both supporting the Formula One World Championships, although the latter is considered to be a feeder series (for young drivers who desire to make the final step to Formula One). The Indy Lights series supports the IndyCar Series, and the NASCAR Xfinity Series and Camping World Truck Series effectively support the top-tier NASCAR Sprint Cup Series. In some series (most notably on oval tracks), the support races take place on both practice and qualifying days, and there is no support race on the day of the feature. A notable example is NASCAR's Sprint Cup Series, where all support races are held on days leading to the feature, although it can be run on feature day if inclement weather forces such.

...
Wikipedia