The phenomenon you are referring to is known as the orbital precession or apsidal precession. Apsidal precession occurs when two objects in slightly different orbits around a central body experience a gradual rotation or shift in the orientation of their orbits over time. This causes the periapsis (the point of closest approach to the central body) and apoapsis (the point of furthest distance from the central body) to gradually change their positions.
The precession of the orbits can arise due to various factors, such as the gravitational influence of other celestial bodies, non-spherical mass distributions, or relativistic effects. These factors cause a slight variation in the gravitational forces acting on the objects, leading to differences in their orbital periods.
It's worth noting that apsidal precession is a general term that encompasses different types of precession, such as nodal precession (when the orbital plane itself rotates) and perihelion precession (specifically for orbits around the Sun). The specific terminology used may depend on the context and the particular celestial objects involved.