What does a flat symbol indicate in musical notation?

A flat symbol in musical notation indicates that the pitch of a note is to be lowered by a half step. When a musician sees a flat symbol placed before a note, they adjust their playing or singing to produce a sound that is just slightly lower than the natural pitch of that note. This adjustment is crucial for achieving the correct harmonic and melodic structure within a piece of music, as it affects the overall tonality and allows for a broader range of musical expression.

In contrast to the other options, which refer to raising the pitch or lowering it by a whole step, the flat specifically pertains to this half-step decrease. Understanding the role of flats is essential for musicians as it informs their interpretation and performance of various musical works.