i always thought it was a woodblock. and compressed or not compressed is kinda immaterial, it doesnt affect the tonal qualities of the hit, only the impact.
A woodblock is a similar-ish sounding but lighter 'tock' sound,(all over the Rapture, an interlude in LCD SS's Daft Punk..., an old-school funk break the Chemical Brothers used on their debut - Birdies Down Beats?) usually used as percussion, not as a main snare sound.
The side-stick snare is the El-B Lyrical Tempo snare, Burial, Al Green's I'm Glad You're Mine (sampled by Massive Attack on Five Man Army, all over Missy Elliot's Sup Dupa Fly), most reggae, etc.
And as noted by Tyro, a rimshot is a snare hit where the stick clangs off the snare's metal rim simultaneously (The Meters, can't think of examples off the top of my head).
Gek-opel mentioned compression it in relation to the Ghost snare sound; I wasn't sure if he was referring to a side-stick or a snare hit.
- sorry for the transmission interruption!
