Janaba bath.

Wa 'alaykumussalam wa ra'hmatullahi wa barakatuhu wa magfiratuhu. One should do janaba bath if he has a wet dream or has sex with his wife or has discharged semen forcefully while being awake . And while a man has sex , exactly at the time when he inserts his private part into his wife's , janaba bath becomes fardh for both of them , even if there is no discharge of semen . During this time it doesn't matter whether he has ejacujalted pre sexual fluid or semen or hasn't ejaculated at all. In this situation , it becomes compulsory for both husband and wife to do fardh ghusl . But in other situations , if a man only discharges pre sexual fluid while emptying his bowels ,(this doesn't mean musterbation , musterbation is forbidden) or while sleeping , he doesn't have to take a janaba bath .

release of semen is only one of the things that break the condition after janabat bath. things like night cycle, getting dirty (like sweating), sinning, sexual encounter also break this condition.