From wikipedia:
Forced orgasm is a form of play where the dominant partner brings the submissive partner to an involuntary orgasm, whilst the submissive attempts to compete with the dominant by attempting to delay the orgasm for as long as possible. Also, the dominant partner may continue stimulation after orgasm, which may cause considerable discomfort to the submissive due to the sensitivity of their genitals. However part of the arousal of the submissive is that after each orgasm they undergo this period of discomfort knowing that pleasure will come shortly after. Part of the attraction of forced orgasms is that the submissive has no control over when and how they receive their orgasm.