What is the term for a symbol added to a note to change its pitch?

The term that describes a symbol added to a note to change its pitch is referred to as an accidental. Accidentals are used in musical notation to alter the pitch of a note from its natural state. This includes raising a note's pitch with a sharp, lowering it with a flat, or cancelling a previous sharp or flat with a natural sign.

Understanding accidentals is crucial in music theory because they are essential for creating expressive dynamics and tonal variation within a piece. Each of the other terms—sharp, flat, and natural—designate specific types of accidentals that modify notes, but the overarching term for them collectively is 'accidental.'