by Lady Bleu
One of the thrills of SM is that it can stretch your limitations. If you enjoy this sort of play, you can naturally find yourself trying more and more new things, accepting greater and greater levels of sensation, doing and feeling more than you've ever done or felt before.
But the process is slow and gradual, and people are not telepathic. It may be that you are the bottom in a whipping scene, and your top is whipping you, and suddenly it doesn't feel good anymore!! and you want them to STOP!!! That is what a safeword is: a word that means "This isn't working! This scene is going wrong somehow! Please stop!"
A safeword needs to be taken seriously. Sometimes you may be playing with a top you don't know that well, and if they do something to you you don't want, it's important that you have a way to let them know, IMMEDIATELY. Especially if you're tied up or otherwise made helpless.
Everyone has their own favorite safeword. Some use "Yellow!" to mean "Something's too intense; I need you to lighten up, but I don't want to stop the scene," and "Red!" to mean "I'm in trouble and I want everything to stop NOW, no more games, scene over, let me outta here!" Some people just have one flavor of safeword, and use "aardvark" or some other weird word they'd never say in the context of a scene. At many parties, the universal safeword is "Safeword!" It's up to you. All it is is a safety valve for when things get out of control. If your top doesn't respect your safeword, it's a safe bet that they won't respect other limits of yours, and you will need to decide whether you want to play with someone who doesn't acknowledge your boundaries.
Using a safeword can be hard to do sometimes. It's important to realize that no one is perfect, and if you as top do something that squicks your bottom (i.e. pushes beyond your bottom's limits--"squick" is a recent bit of s.s.b-b jargon), it doesn't mean you're a bad lover or a bad person. It only means that you ran into a limit you didn't know was there, or you were tired or disconnected and not in tune with your bottom. It happens to everyone from time to time. If you as top feel burned out and want to stop the scene suddenly, or you get a powerful reaction you weren't expecting and aren't sure how to continue, you can use a safeword too; safewords aren't just for bottoms! If you as bottom feel like your top is pushing you, and you don't want to play anymore, it's not fun, that's when you want to use a safeword--your top will be glad you used it to tell them where you were at.
A safeword is just a communication tool, nothing more, nothing less. If you're playing intensely, it may feel hard to stop the scene, to come back from the edge via a safeword... but if you need to, that's what they're for. Some tops deliberately push their bottoms until their bottoms call safeword; this way, the bottom gets the experience of using it. A safeword that's never used can seem unusable, which isn't a good property for a safeword.
Sometimes a top will want to gag you, whether because you're being too noisy or they want to increase your helplessness or you've been being impertinent or whatever. You may still want a safeword to let the top know when a rope is too tight or the nipple clamps are pinching or whatever. Some people put a handkerchief in the bottom's hand; if they let go and the handkerchief falls, they know there's something up.
Before playing with someone, it's a good idea to negotiate, not only what safeword you want to use, but how you'll handle it if you need to use the safeword. When you're just getting into SM, it's almost inevitable that some scenes will end prematurely or abruptly. If you acknowledge this possibility in advance, and talk about what kinds of comforting or remedy you might like, it'll make recovering from a mishap a lot easier and more pleasant. And because a scene goes wrong is no reason to think that you or your partner is fundamentally bad or untrustworthy--mistakes will happen. (If your partner doesn't want to hear your concerns about the mishap, though, or if they belittle or deride your concerns, you may well be unable to avoid future mishaps. If your relationship doesn't learn from painful experience, it may not be ready to handle doing SM. Of course, this kind of processing is a vital part of 'every' healthy relationship, SM or not.)
Not every SM player uses safewords. Some people into SM don't find them useful for the style of play they prefer; more straightforward communication suffices for them. Some partners find their need for a safeword gradually diminishes as they come to know each other better. Some people do SM in which the bottom doesn't 'want' to have a verbal escape route, for the duration of the scene. (This "no-safeword" play is also sometimes called "edge play.") One thing that you will learn about the BDSM scene is that styles vary wildly, and peoples' experiences are astonishingly diverse. But for many people beginning their explorations (and many who've explored enormously), safewords have proved very helpful.