Let's talk safe words!
Safe words are super super important and I don't think enough people talk about it. They aren't only for subs either, doms should also have a safe word because communication and boundaries are important.
Off the bat let's talk about words like, no, stop etc. In a vanilla setting these could work but with kink it becomes more of a blurred line. Especially if you're someone like me who is into things like overstim or detail where sometimes you say those things but you don't mean it. There's a whole bunch of kinks this applies to as well so it's always safer to chose something you wouldn't normally say.
It could be a singular word but the way I do it is the traffic light system. It's a way for my partner to check in aswell by asking "what's your colour?". So here they are.
Red - stop everything, we're done, I can't/don't want to continue
Yellow - pause, maybe we need to talk about something really quick or reposition, sometimes it's just that I need water
But if you're using anything like breath play or gagging you NEED a nonverbal que. I also use mine for if I go nonverbal during sex or can't form words properly due to headspace.
Tapping once is green, tapping twice is yellow, tapping three times is red.