Many terms are used to describe the S/M subculture Kink, Leather, Fetish, BDSM
Kink is generic term used to describe the world of S/M play and people. A person is said to be kinky if having unusual sexual practices or turn-ons.
Fetish is commonly used to refer to an object that is erotically arousing for a person, also can be used to describe an activity that is arousing. Also used to describe style of clothing, as in Fetish-wear, which can include leather, PVC, corsets, high heels, collars, etc.
BDSM stands for Bondage, Domination, Sadism, Masochism
Bondage enjoying the sensation of being restrained, or tied up
Domination also symbolized as D/s for Dominance/submission, for play that involves one person in the Dominant/power role and the other in the submissive/obeying role
Sadism A Sadist is someone who enjoys hurting others. Very few people are truly sadistic, which also can imply enjoying cruelty for its own sake. I think it is more true that kinky people enjoy bringing each other pleasure, albeit through painful methods
Masochism A Masochist is someone who enjoys being hurt or experiencing pain. Again, not may people are purely masochistic, rather, they enjoy the effect of going through pain to experience something pleasurable, intense, transforming, etc.
Safeword Often, a fantasy is to protest No or Stop while something is being done to you, but to be forced to accept the experience anyway by the dominant. A safeword is a word that is agreed upon at the beginning of a scene, which, when used by the submissive/bottom will mean for all interaction to come to a stop. Sometimes people use the words Red to stop entirely, Yellow to slow down or decrease the intensity, or to pause the action, and Green to indicate that everything is fine, more would be OK, or keep going with what is happening.
Top used to refer to the person in a scene who is giving, doing, or commanding, also can be called the Dominant.
Bottom used to refer to the person in a scene who is receiving or obeying, also can be called the submissive.
Master / Mistress not everyone likes to be called these terms, sometimes a Master/Mistress title is only used between people who have negotiated a contract of service. Always ask how your play partner would like to be addressed.