A "countermovement jump" refers to a type of jump where you first drop down a little before jumping up. It gives you more power and height in your jump. Full definition
The half squat group improved countermovement jump height by more than the front step group, and there were no other differences between groups. (strengthandconditioningresearch.com)
Plyometrics: single leg and double leg jumps such as hops, bounds, repeated broad jumps and countermovement jumps hurdle hops, depth jumps, drop jumps etc.. (rugbystrengthcoach.com)
The slow SSC involves longer contraction times (0.25 - 0.50 s), larger angular displacements and can be observed in exercises such as countermovement jumps or box jumps. (epicertification.com)