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 form such ratios and the orbital periods of 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).
A Secular Resonance is a resonance of orbits not on each "go round" but on a longer-term (Secular) pattern. It might show up as a pattern in the orbits' Precessions. The term is common in analysis of the orbits of Asteroids and other Minor Planets.
Corotation Resonance (CR)
Kuiper Belt (K Belt)
Late Heavy Bombardment (LHB)