Sim

A sim is essentially a server in Second Life (they actually pack 4 standard sims to an actual server box and 16 OpenSpace sims onto one server). It hosts a fuckton of land and runs physics and shit.

Sims are still vulnerable to being crashed by some things. At the time of this writing, all sims are using Havok 4 as their physics engine which pretty much can't be killed by physics overload. It just lags into hell.