Viola
The Viola is a non-transposing Alto instrument from the Orchestral String family.
The Viola is unique in that it uses the Alto Clef as it’s default clef as this suits the lower range from C2 best. In it’s upper register (up to A6) it reads Treble Clef as to avoid excessive ledger lines.
The Viola sits one fifth lower than the Violin and one octave higher than the Cello. It forms an integral part of filling out an orchestral string sound but as an alto instrument, is usually treated as a harmonic voice rather than a melodic one.