Stationkeeping (or station keeping) is the operation of a spacecraft to keep it in its intended orbit. There are numerous factors that can make an orbit degrade (make the spacecraft tend to change orbits), some being the gravity of a third body, tidal forces, atmospheric drag (e.g., from the thin but very extensive upper atmosphere), and radiation pressure. Given these, operation of a spacecraft virtually always requires attention and intervention, tracking its position and planning and carrying out corrective maneuvers. Low Earth orbit is especially affected by the drag of the atmosphere.
The term stationkeeping is borrowed from a similar operation of ships on the waters, i.e., keeping a ship at a location, or at its place in a formation and the term orbital stationkeeping is sometimes used to distinguish the two.