Tuning is making each string in the piano vibrate at the correct pitch when struck by its hammer. The strings (there are well over 200 of them!) are wound around a tuning pin which is turned by a tuning hammer or tuning lever by the technician.
Tuning is NOT fixing a sticking key or any other problem, although often some minor problems are fixed during the course of a tuning.
Most manufacturers recommend that their pianos be tuned twice per year. It seems obvious to say, but a regularly tuned piano stabilizes better and doesn't go as far out of tune between tunings as a neglected piano.
If it has been years since your piano has been tuned, it will very likely require a "Pressure Correction" before a fine tuning can be administered. It's something like tuning—the same actions are taken—but the main goal of a pressure correction is to re-establish correct pressures on the strings, bridges and plate.
For more information on piano care in general, go to the Piano Technician's Guild website.
Call for a tuning today at 406-594-1985, or if you live in the Helena area, you can book online here.