BDSM is an umbrella term for a variety of (often erotic) practices or roleplaying; it is an acronym representing three components:
BD: Bondage & Discipline (playing with physical restraints, training, punishment, etc.)
DS: Dominance & Submission (playing with obedience, power exchange, service, humility, etc.)
SM: Sadism & Masochism (playing with pain, degradation, fear, etc.)
More often than not, other 'deviant' sexual practices are also considered to be part of BDSM.
BDSM is a consensual activity respecting the fundamental rights of every human being involved; this separates it from sexual and domestic abuse.
Everyone is different, and finding two kinksters with the exact same preferences is more info probably impossible. There are however a few common 'archetypes' that people can identify with to varying degrees (from 0% to 100%). Curious to what extent each archetype suits you? Take the test! The list below is by no means complete but it should cover the most common ones.