The alto clef is a type of musical clef used primarily for instruments that play in the alto range, such as the viola. It is represented by a stylized letter "C" placed on the second line of the staff, indicating that this line represents the note C4. This clef helps musicians read music more easily by positioning the notes they commonly play on the staff. In orchestral music, the alto clef is essential for composers and arrangers when writing parts for instruments like the viola and certain brass instruments. By using the alto clef, musicians can read and interpret music without excessive ledger lines, making it more accessible for performance.