From the Piano Technicians Guild:
… It’s important to note that tuning is only the adjustment of the system of strings and pins that determines the pitch of each string. Your piano also requires a periodic servicing called regulation…
What is piano ‘action’ regulation and how does it affect my piano’s performance?
Regulation is the adjustment of the mechanical aspects of the pianos to compensate for the effects of wear, the compacting and settling of cloth, felt, and buckskin, as well as dimensional changes in wood and wool parts due to changes in humidity…
… The action is the mechanical part of the piano that transfers the motion of the fingers on the keys to the hammers that strike the strings. It is comprised of over 9,000 parts which require adjustment to critical tolerances to be able to respond to a pianist’s every command…
Every note in a grand piano has more than 35 points of adjustment.
Every note in a vertical piano has over 25 points of adjustment.