Modulation in music refers to the change from one tonality or key to another). It can be used to create structure or form in a piece of music, as well as add interest and evoke different emotional responses from the listener). Modulation can occur in various ways, including:

• Direct modulation: This is when the music changes key abruptly, without any transitional chords.
• Pivot-chord modulation: This is when a chord is used that is common to both the original key and the new key, acting as a pivot between the two.
• Melody-driven modulation: This is when the melody itself leads the listener to expect a change in key, and the harmony follows suit.
• Transitional modulation: This is when a series of chords are used to gradually transition from one key to another.
• Combination modulation: This is when two or more of the above techniques are used together.

Modulation can also involve changes in other parameters, such as tempo, timbre, or spatial location of sound). In pop music, modulation is often used to add power, momentum, or intensity to a section of music.