These folks administrate systems. WLUG has a lot of them.
That mainly means that they manage networks - routers, servers, firewalls etc. They have the power and responsibility to install and configure software. They do the drudgework to keep the machines running (clear out disk space, watch logs, organise backups, etc). They often write scripts to automate (parts of) these tasks.
System administration gets fun when you are trying to manage tens, hundreds or thousands of machines. You don't have the time to manually fix each machine separately. You need to organise ways of treating all the machines as if they are identical (but beware of Murphy). Lotsa fun. Even managing 10 machines gets complicated fast. The art of system administration is being able to manage all this. The easiest way of doing is to be as lazy as possible. The LazySystemAdministrator makes her life easier by automating as much as possible so she needn't touch each machine separately.
A lot of LUGers are interested in doing things like automated ways of handling mail for potentially thousands of users in a scalable way, handling DNS, or organising large networks.