Sorry if this isn't within the rules, lurked but haven't posted here.

The WSBK (Superbike World Championship) began in 1988. This is production motorcycle (opposed to prototypes see: MotoGP), closed circuit (opposed to public roads see: Isle of Man TT) racing.

One point that differentiated it from many other top level motorsports, until recently, was that they would hold 2 races on the Sunday of a race weekend. The championship's main, and recently more popular, rival is MotoGP (formerly 500GP). They hold only one race on the Sunday.

The WSBK has always had more of an "everyman" feel to it, partly because a lot of club racing (casual/local racing) also holds multiple races for the same class in one day.