The Roche lobe is a concept in astrophysics that describes the region of space around a star within which material is gravitationally bound to that star rather than being pulled away by another nearby star. This concept is particularly important in binary star systems, where two stars are close enough to affect each other's gravitational fields. Understanding the Roche lobe can help astronomers explain phenomena such as mass transfer, accretion disks, and the formation of binary star systems.