A promoter is someone who publicizes an event on behalf of the participants of said event. Typically, such persons are compensated by being given a percentage of the money generated by the event.
In 2370, Quark claimed to be the exclusive promoter of Julian Bashir and Miles O'Brien when he created a scheme to increase business at his bar. He lured both men into playing a racquetball match by publicly claiming that they were doing so to raise money for the Bajoran War Orphans Fund. The money would be generated by spectators betting on the outcome, and the proceeds not paid out to the winners would be given (minus a fee to the House) to the Fund. Bashir later persuaded Quark to give up the fee he intended to take to the Fund as well. (DS9: "Rivals")