Fill (music)
short musical passage, riff, or rhythmic sound
A fill in popular music is a short instrumental passage, between melody lines of a song. (A longer passage between verses is called a solo.)
Fills are usually played with a keyboard instrument or a guitar, but other instruments (such as a saxophone) may also be used. Drum fills are sometimes called "drum rolls", but a roll is actually a steady beat on a single drum, while a fill may use more than one drum or beat.