The cello or violoncello is a bowed (and occasionally plucked) string
instrument of the violin family. Its four strings are usually tuned in
perfect fifths: from low to high, C2, G2, D3 and A3. The viola's four
strings are each an octave higher. Music for the cello is generally
written in the bass clef, with tenor clef and treble clef used for
higher-range passages.
Learn more about the cello on Wikipedia!