Pattern or order of striking sticks to a drum. The patterns will indicate which hand is used to initiate the stroke for each note of the pattern. An "L" beneath (or over) the note indicates that the left hand is to be used and an "R" beneath (or over) the note indicates that the right hand is to be used.
One exception to this is the group of multiple bounce rolls. With these rolls, a series of "L's" or "R's" indicate the number bounces of the drumstick after the initial stroke. The first "L" or "R" indicates the initial stroke and all subsequent letters indicating the same hand would indicate bounces.