Combination of 2 words, "orgasm" and the slang term "zzz." Meaning having multiples orgasms to the point of exhaustion. Utimately putting you to sleep.
Yo dawg, me and my girl had so many orgasmzzz that we knocked the fucked out.
To ejaculate in such a quiet or subtle way that your partner either barely noticed or did not notice at all.
girl: why did you stop?
guy: rolls off
girl: WTF. Did you cum?
guy: yeah
girl: I couldn't tell. That was quiet.
guy: Like a ninja. I guess i ninjaculated.