Brazilian Jiu-Jitsu is a martial art and combat sport thats focus is placed on grappling and ground fighting. It was derived from the Japanese martial art of Kodokan Judo in the early 20th century, which was itself then a recently-developed system (founded in 1882), based on multiple schools (or Ryu) of Japanese jujutsu. 

The legendary Gracie family is responsible for developing jiu-jitsu to reflect modern street fight situations in Brazil.  They placed jiu-jitsu on a world stage and showcased it's effectiveness through events like the Ultimate Fighting Championship, a competition putting one style of martial art against another in a no rules situation.  Jiu-jitsu quickly earned it's reputation as the "King of the Martial Arts".

Jiu-Jitsu promotes the principle that a smaller, weaker person can successfully defend themselves against a bigger, stronger assailant using leverage; most notably, by applying joint-locks and chokeholds to leave an attacker seriously injured or unconcious.

Brazilian jiu-jitsu has proven to be the most effective martial art through recent decades of no rules competition.  With 9 out of 10 fights ending in a clinch or on the ground, the skill set learned in jiu-jitsu is necessary in order to defend oneself.  Brazilian jiu-jitsu tournaments were developed to practice the techniques of jiu-jitsu in a controlled enviroment.  Points are awarded for gaining superior positions. A submission, or the tapping out of your opponent, signals the end of the contest.

Submission

The majority of submission holds can be grouped into two broad categories: joint locks and chokes. Joint locks typically involve isolating an opponent's limb and creating a lever with the body position which will force the joint to move past its normal range of motion. Pressure is increased in a controlled manner and released if the opponent cannot escape the hold and signals defeat by submitting. In a tournament format opponents can indicate submission verbally or they can tap out (i.e. tap the opponent, the mat several times. A choke hold, disrupting the blood supply to the brain, can cause unconsciousness if the opponent does not submit soon enough.