Ah, do you remember or perhaps saw dogs mating and the two of them got stucked. Like, ashdgjakdlnd can't explain but yeah knot is something like that when two person/species are mating and they got goddamn stucked for a minute or 2(or hours) idk I forgot when I searched it I think when the dicc reaches the climax and it swelled up
Kind of like a bulbus glandis (bulb type thing) in an Alpha’s penis that swells when they are aroused and keeps them locked inside their Omega during sex to increase chances of getting the Omega pregnant.
Just like a dog when they making love (=・ω・=)
If you still don't understand you can search at google :3
Sorry for the question but what knot / knotting means