Locking
Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the bodies reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit.
In the case where a tidally locked object possesses synchronous rotation, the object takes just as long to rotate around its own axis as it does to revolve around its partner. For example, the same side of the Moon always faces Earth, although there is some variability because the Moon's orbit is not perfectly circular. Usually, only the satellite is tidally locked to the larger body. However, if both the difference in mass between the two bodies and the distance between them are relatively small, each may be tidally locked to the other; this is the case for Pluto and Charon, and for Eris and Dysnomia. Alternative names for tidal locking are gravitational locking, captured rotation, and spin–orbit locking. The process that ends in tidal locking is called tidal despinning, which ends in a tidally despun body.
Text adapted from Wikipedia, CC BY-SA 4.0.