Attack is the attack time constant for the slow attack/release filter
Attack fraction (or ratio) is the percentage of the attack time constant that will be used for the fast attack/release filter. Used to work on the transient at the beginning of a sound.
Release is the release time constraint for the fast attack/release filter (as the release time has to be higher)
Release fraction (or ratio) is the percentage of the release time constant that will be used for the slow attack/release filter (as it has a faster release time constant). Used to work on the transient at the end of sound.
Slope is the ratio, 1 being the identity, higher than 1 compressing the transient, less than 1 swelling it
Softness is an indicator of the harshness of the knee of the underlying compressor
Color is an indicator of the color around the threshold: positive increases the gain around it, negative decreases it
Quality is the amount of color
Make-up is the gain after the effect
Dry-wet gives the balance between the unprocessed signal and the processed signal