Piano tuning is the act of making minute adjustments to the tensions of the strings of an acoustic
piano to properly align the intervals between their tones so that the instrument is
in tune. The meaning of the term 'in tune', in the context of piano tuning, is not simply a particular fixed set of
pitches. Fine piano tuning requires an assessment of the vibration interaction among notes, which is different for every piano, thus in practice requiring slightly different pitches from any theoretical standard. Pianos are usually tuned to a modified version of the system called
equal temperament (see:
Piano key frequencies, for the theoretical piano tuning).