I have seen ukemi defined a couple different ways:
1. Rebounding from the ground: This would encompass all rolls, break falls and etc methods for falling safely.
2. Another way it is used in Japanese arts is the Uke /Tore relationship . In this training format you have an attacker (usually the Uke) and the defender (Tore). Uke initiates the aggression and then is required to "take a fall" while an appropriate technique is applied. It is the responsibillity of the Uke to give a convincing attack with the correct intention and yet still remain somewhat non-combative as the tore applies any given technique. Again Uke is receiving the technique.
Hope this helps.
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