What is the difference between tuning and regulation?
Tuning adjusts the pitch of the strings. Regulation adjusts the mechanical action — how the keys feel and respond.
Tuning a piano means adjusting the pitch of the strings so that every note sounds at the correct frequency.
Regulation refers to the adjustment of the touch — specifically the way the keys feel and respond to your playing. There is an intricate mechanical apparatus called the action, which comprises many small moving parts hidden between the key and the hammer that strikes the string. Regulation ensures that these parts are in good condition, properly aligned, and operating smoothly.
Both tuning and regulation should be performed by a qualified piano technician.