Xxx2srv_d with the right description?

Hello,

i read in QGC the description for roll2srv_d, yaw2srv_D or ptch2srv_d.
There is a description “damping gain”.
Is it right? Or shall this be “diff gain” for PID.and if i wrong, what is the parameter for diff?

6h later… i belief ardupilot has no diff.
The docu for “Pitch, Roll and Yaw Controller Tuning” shows no diff.
And that is interesting.
Wy you chose this kind of controller?

Thanks