A dry orgasm.
Generally occurs after an excessive amount of wet (conventional, ejaculatory) orgasms in too short a period of time. The testes lack the requisite time to "recharge" and thus no ejaculation accompanies the climax.
Also possible: a discharge void of sperm, comprising only the fluids, released by the prostate, through which sperm are carried. This discharge would be clear in color, much smaller in volume as compared to a regular ejaculation, and much less viscous.