Repetition is when sounds, sequences or phrases are literally repeated immediately.
Some songs that use repetition ↓
Imitation is the repetition of a melody or idea shortly after its first appearance in a different voice, often at a different pitch.
Inversion is when an idea is heard exactly upside-down or “mirrored” across a horizontal plane, like mountains reflected in a lake.
A musical pattern that repeats itself over and over again - often whilst other things are going on over the top...