Tori's merging with uke's movement
Awase literally means "coming together" or "matching up". As aikidō is the art of the controlled "unification of energies", awase is a central principle of the martial art. Tori's reaction is a fusion with uke's attack energy, with tori taking the leading role in this joint movement.
The term is often translated as "blending of the movements", but this does not do awase justice, as it makes tori's role appear rather passive.
The notion of awase is closely connected to that of atari, the point of (first) contact.