Meaning of MODULATION in English
In music, the transition from one mode or key to another.
There are three principal methods of modulation in classical harmony: diatonic, in which a pivot chord is common to both keys; chromatic, in which the notes of the pivot chord are altered by a semitone; and enharmonic, in which the notes of the pivot chord, while retaining their original tones, simply assume different names. Modulation may be transitory, as in the course of thematic development, or structural, contributing to the harmonic definition of the form.
Britannica Concise Encyclopedia. Краткая энциклопедия Британика. 2012