Judo is a martial art that originated in Japan. The focus of Judo is to throw, sweep, or trip your opponent. Judo also includes pin down holds, chokes, and submissions such as arm bars and joint locks. For more information check out https://judoinfo.com/
Judo is an olympic sport and can be spectacular to watch.
Sport judo prohibits some of the techniques of traditional judo that you might use in self defense scenarios. Notice the attack on the legs in this video.