The LISA conference is the primary System Administration conference held annually by Usenix (the Unix Professional Socity) and its affiliate, SAGE (the System Administrators Guild). It has been held each year since 1987, and the location alternates between the Eastern and Western US.
"LISA" stands for "Large Installation System Administration," but the name refers to a time when a "large system" was one with more than twenty users, or more than 1 gigabyte of disk space. These days, the conference deals with all aspects of Unix system administration.
The first three years of LISA were "workshops" of a few days' length, and in 1990 it was first termed a "conference". These days the conference is six days long. The first three days consist of tutorial sessions, either half-day or full-day lectures on either new materials of interest to Unix administrators, or older topics that deserve continuing examination. The final three days of the conference consist of various discussions, presentation of papers, and talks by invited guest speakers.
A highlight of the evenings are what are termed "BOFs", meaning "birds of a feather" sessions. These are not planned in advance by the conference organizers, but rather can be suggested by any attendee and posted on the conference bulletin boards. They are essentially "ad-hoc" discussion forums on topics of interest that were not covered in the main conference sessions, and in the past have dealt with spam control, industry ethics, and Unix certifications.
Information on past and upcoming LISA conferences is available at the Usenix web site, at http://www.usenix.org/events/bytopic/lisa.html.