What is a safeword in BDSM

A safeword is a codeword or series of codewords that are sometimes used in BDSM for a submissive (or "bottom") to unambiguously communicate their physical or emotional state to a dominant (or "top"), typically when approaching, or crossing, a physical, emotional, or moral boundary. Some safewords are used to stop the scene outright, while others can communicate a willingness to continue, but at a reduced level of intensity. Safewords are usually agreed upon before playing a scene by all participants, and many organized BDSM groups have standard safewords that all members agree to use to avoid confusion at organized play events.

Safewords are generally used by those whose practice of BDSM falls under the guiding philosophy of safe, sane and consensual. Those who practice the more permissive philosophy of risk-aware consensual kink may abandon the use of safewords, especially those that practice forms of edgeplay or extreme forms of dominance and submission. In such cases, the choice to give up the use of safewords is a consensual act on the part of the bottom or submissive.

Sources: Wikipedia