This post is part of an effort to provide a glossary for novice submissives of words commonly seen across this site and in the BDSM community.
Discipline has two distinct definitions in relation to BDSM.
Discipline is the part of training that is a preventative correction of behavior. You can undergo discipline to keep focused and in the right mindset. Discipline can take on many forms from writing lines to a spanking or corner time. It is usually performed in a regular basis, sometimes scheduled and is meant as a positive reinforcement.
Discipline can also mean the specific rules, rituals and protocol in place for the submissive. In this way submission is the discipline. You need to work to master a discipline as a path in life.