roll

1. A tremolo effect performed on a drum (or almost any percussion instrument) using a continuous series of strokes. In short, the roll is a method to produce a sustained sound on a drum. Rolls are used on other percussion instruments such as the marimba and the xylophone to sustain the sound. There are a numerous ways to produce a roll and there is an entire group of rolls as part of the standard list of drum rudiments. The most common types of rolls are the single stroke roll, the multiple bounce roll also known as the long roll, and the double stroke open roll.
2. A musical ornament that directs the musician to perform the indicated chord as an arpeggio or broken chord.

See more about single stroke roll rudiments in the Appendix. 

See more about multiple bounce roll rudiments in the Appendix. 

See more about double stroke open roll rudiments in the Appendix. 

See more about ornaments in the Appendix.