Orbital Resonance is typically the settling of orbits of two or more bodies so that their orbital periods are related by two small integers. This happens when the forces of Gravity when they are nearest tend to push them toward such a position, i.e., negative gravitational feedback.
The orbital periods of three of Jupiter's Moons have a ratio and the orbital periods of and Pluto and Neptune have a ratio of 3:2. Such a resonance, where there is a simple integer ratio between the periods is called a Mean Motion Resonance (MMR).
Corotation Resonance (CR)