Brazilian jiu-jitsu (BJJ) is a self-defence martial art and combat sport based on grappling, ground fighting, and submission holds. BJJ approaches self-defense by emphasizing taking an opponent to the ground, gaining a dominant position, and using a number of techniques to force them into submission via joint locks or chokeholds.

BJJ eventually came to be its own defined combat sport through the innovations, practices, and adaptation of Gracie jiu-jitsu and Judo, and became an essential martial art for modern MMA. Governing bodies such as the International Brazilian Jiu-Jitsu Federation worldwide, and set the rules and standards to be held in sport BJJ competitions.

BJJ revolves around the concept, taken from traditional Japanese jūjutsu, that a smaller, weaker person can successfully defend themselves against a bigger, stronger, heavier opponent by using leverage and weight distribution, taking the fight to the ground and using a number of holds and submissions to defeat them. BJJ training can be used for sport grappling and self-defense situations. Sparring, commonly referred to as "rolling" within the BJJ community, and live drilling plays a major role in training and the practitioner's development. BJJ can also be used as a method of promoting physical fitness, building character, and as a way of life.

Source: Wikipedia