1) The proper, real definition of the word "Judo" is that it is a Japanese martial art. It is a sport adapted from jujitsu, which uses principles of not resisting, and is similar to wrestling.
2) A dumber, but also valid for this Urban
Dictionary, version of the word Judo means "you don't", and is said by sterotype rednecks. It is mentionned at least once on the show "Blue Collar Comedy", and also in jokesites that have a '
redneck dictionary'.