The ability to modify attitudes and behaviours to fit changed or changing circumstances.

Discussion

For me, this differs from flexibility in that adaptation is sticky. In other words, flexibility is a temporary bend that eventually bounces back to normal. On the other hand, adaptability means you are able to mold yourself into a new form that sticks until the next change of circumstances.

A spring will bend but bounce back (flexibility), but a metal coat-hangar will hold its new shape (adaptation).