Ukemi is the reaction of uke to a technique, especially in the sense of rolling or falling. The word literally means "receiving".
Rolling and falling is practised with and without a partner. The goal is to make it as natural and smooth a movement as possible, in order to reduce the impact.
Particularly soft forms are often called "feather fall"; the Aikido teachers Frank Ostoff and Jan Nevelius Shihan have developed an elaborated curriculum for their practice.
