text: Well, I'll try to be clear. Yes, it's semen (and only it!)\nThat event is called male orgasm and it occurs when the excitment reaches the apex. Mind sends signal and from Prostate and Testicles (and from other glans too) semen begins to come out (through the urethra). It's a fast event lasting few seconds even. And after 1 -2 min. penis become flabby again. I hope to have satisfied your question.