What is the musical term for a change of key?

The term for a change of key in music is modulation. Modulation involves shifting from one key to another, creating a sense of contrast and variety within a musical piece. This can enhance the emotional impact of the music and is often used to develop themes or sections within a composition.

While transposition refers to changing the pitch of the entire piece or a section of music by moving it up or down to a different key, it typically involves maintaining the same musical relationships rather than creating new ones as modulation does. Transition, on the other hand, refers to a passage that leads from one section of music to another, rather than a change in key. Variation involves altering a melody or theme, but it does not inherently involve changing the key itself. Thus, modulation is the correct term associated with the concept of changing keys within a piece of music.