Modulation in music is the process of changing from one key or tonal center to another within a piece. This shift can be accompanied by a change in key signature but does not have to be. Modulation serves to create structure, add interest, and convey different emotions in music by moving the tonal focus from one key to another

. Key points about modulation include:

• It involves a change in the tonic or tonal center, which is the "home" key of a piece.
• Modulation can be gradual or abrupt and may use transitional elements such as pivot chords (chords common to both the original and new key) to smooth the transition.
• If the music briefly suggests a new key but quickly returns to the original, this is called tonicization, not true modulation

• There are various types of modulation, including common chord modulation, chromatic modulation, parallel modulation, and direct modulation, each with different techniques for shifting keys

In summary, modulation is a fundamental musical technique that enriches compositions by changing the key center, thereby enhancing variety and emotional expression in music.