key
The tonal center of a piece, defined by a scale and its tonic note.
In Depth
A key defines the tonal center of a piece — the note and scale that feel like home. A piece in C major uses the C major scale as its foundation, with the note C providing the strongest sense of resolution and stability. Keys can be major (bright, stable) or minor (darker, more complex).
The key signature at the beginning of a staff tells performers which notes are consistently sharped or flatted throughout the piece. Composers choose keys deliberately — trumpet-friendly keys like D major and B♭ major sound bright and festive, while flat keys like A♭ major and E♭ major are often associated with warmth and richness.
Before equal temperament, each key had a distinct character. Composers chose keys carefully — D major was considered brilliant and martial, while E-flat major was heroic and romantic.