In n-body gravitational systems, possibility of close gravitational encounters exists, and is in fact, quite common. Whenever two bodies get close (close is a relative term here, and it is a function of the masses of the interacting bodies), they will exchange energy and momentum. This leads to alteration of their original trajectories. The dramatic nature of these alterations is what leads to this being called scattering, and can be desirables in cases like gravity assists.