Contrary to popular belief, a rim-shot is not a drum riff...It is the sound made when the stick hits the drum at a shallow angle to hit both the skin with the tip of the stick, and the rim with the length of the stick at the same time, causing a louder and sharper sound. Sounds best on the snare drum.
It is usually used as an accent to...ehm...accentuate (sorry!) the start or end of a bar or simply when the drummer feels it's necessary.
I think that the original creator of this node was referring to a Buzz Roll. This is the sound normally associated with the suspense type of roll at a circus, beheading ceremony on TV etc..It is a more constant sound caused by a light and repetitive, alternate bounce of the sticks on the snare drum skin. Rather difficult to achieve for an inexperienced drummer like myself.