The term denotes an exercise in 取り tori, applying technique to a random ( 乱 ran) succession of uke attacks.
In judo, jujutsu, and Shodokan aikido, among others, it most often refers to one-on-one sparring where partners attempt to resist and counter each other's techniques.
The term was described by Jigoro Kano, the founder of judo, in a speech at the 1932 Los Angeles Olympic Games: "Randori, meaning "free exercise", is practiced under conditions of actual contest.
The two combatants may use whatever methods they like provided they do not hurt each other and obey the rules of judo concerning etiquette, which are essential to its proper working.
Although in karate the word kumite is usually reserved for sparring, some schools also employ the term randori with regard to "mock-combat" in which both karateka move with speed, parrying and attacking with all four limbs (including knees and elbows).