If legato means to be played without any perceptible interruption between the notes, non-legato means to be played with a perceptible interruption.
Non-legato differs from legato in that a break is perceptible (that is, a break is present). It differs from staccato, however, in that a break is merely perceptible (that is, the break is not very large).
Other terms are used for a non-legato touch, each one with its own subtle implications: