The vast majority of major pianos cover a range that spans from A0 to C8; this is equivalent to seven octaves plus a minor third. An octave is a musical interval that exists between one note and another note that has either double or half of its frequency. In Western music, the distance between octaves is 12 semitones.
The octave is the most consonant interval in music. A minor third is the interval between two notes that are three semitones apart, and it is somewhat dissonant. Modern pianos typically cover the range between A0 and C8, but some older pianos historically only covered the range between A0 and A7. With modern construction techniques, this range is not because of physical limitations; it is primarily a result of musical convention. In fact, some modern pianos extend the conventional range. For example, there are pianos that extend the range down to F0.