The Roche Limit

The Roche Limit is the radius inside which a satellite, held together only by its gravity, will disintegrate under the tidal forces of the body about which it is orbiting.

Online references:
Wiki: Roche Limit

Roche Lobes

When you draw a set of equipotential curves for the gravitational potential energy for a small test mass in the vicinity of two orbiting stars, there is a critical curve shaped like a figure-8 which can be used to portray the gravitational domain of each star. If you rotate the figure-8 around the line joining the two stars, you produce two lobes known as Roche lobes, after the French mathematician Edouard Roche.