BDSM stands for “Bondage & Discipline” (BD), “Domination & Submission” (DS) and “Sadism & Masochism” (SM). However they don’t have to be used in the same situation, for example, you could have Domination & Submission with Bondage and not have Discipline and Sadism & Masochism.

Bondage and Discipline is about tying someone up and/or inflicting a level (high to low) of pain to them. The bondage doesn’t have to be restrictive and the discipline doesn’t have to be about pain, it could be about not being able to orgasm (chastity).

Domination and Submission (Dom and Sub) is basically two people (can be more, but is very commonly 2), one is dominant and tells the other person what to do, the other person being the submissive who takes the orders and does what the Dom says. In most cases the Dom and Sub have a healthy and loving relationship between them and are taking bondage and discipline to a higher level.

Sadism and Masochism is all about either receiving pain (Masochism) or inflicting pain (Sadism) to another person and in both cases the person gets sexual satisfaction from doing it or receiving it. This can tie in with the other elements of BDSM, like bondage for example.

~ from wikinut.