"I would do anything for love, but I just won't do that."
-->Meatloaf

A safeword is a word or phrase intended to signify a hard "no" in BDSM play. As bondage involves giving up some consent, the word "no" is usually used in a roleplay setting. A safeword really means "no"; ignoring a safeword is a massive breach of trust and conduct. The submissive partner has the safe word to be, ahem, safe. Usually consisting of three syllables; with a tier system. The first syllable is a go-ahead. The second syllable means they're not quite comfortable, but they're willing to try. All three together is a flat refusal. It may be advisable to choose a mood killer to convey that this utterance means business (or rather, an end to "the business").