NLP stands for Neuro-Linguistic Programming, (started by 2 talented people; Richard Bandler and John Grinder). It started from studying what makes successful people successful. What are their belief, their psychology, their states. They come up with the conclusion that  Body and mind are one. For example when you are uncertain about something (low in confidence), your body naturally will not up right(maybe a bit slumped to the front), and words used are on the pessimistic, negative side) That is, NLP describes how your language & your mind (neuro) affect your behavior.