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'.