pivot chord
A chord that belongs to two keys simultaneously, facilitating a smooth modulation
In Depth
In common-chord modulation, the pivot chord serves as the hinge between the old key and the new. It is analysed with dual Roman numerals: one in the departing key and one in the arriving key. The smoothest modulations use pivot chords with strong functional meaning in both keys. Closely related keys share more potential pivots, which is why modulation to the dominant or relative major is so natural. Pivot chord modulation is the most common modulatory technique in Classical-era music.
Schubert was famous for finding unexpected pivot chords between distant keys, creating his characteristic harmonic wandering.