Droop is when the wheel travels below the position it holds when the car is at rest.

Compression is when the wheel travels up, into the wheel well.

In the case of shocks, there is:
* Bump -- when the shock shaft travels into the body
* Rebound -- when the shaft extends from the shock body.

Both of these can be broken down into high-speed and low-speed. In addition there is also "blow-off"( if my memory is correct) which is the condition when there is a large highspeed compression such as hitting a curb. This is a different condition from high-speed which relates more to controlling the wheels travel over rough surfaces like coblestones. Low speed has to do with the control of the chassis as the car pitches and leans.