Kinktionary
More like guidelines and a lot less like definitions.
ashtray
A submissive BDSM role in which a person serves as an ashtray for a Dominant partner. This generally involves sprinkling the sub with ash, or cigarettes or cigars being put out on the person's skin, mouth, or other areas.
Note that even ash can be quite hot, and cigarettes and cigars can cause significant burns. Being an ashtray is therefore a risky form of play that should involve carefully negotiated consent (and caution!). See Risk Aware Consensual Kink.