RLM (AKA Robert Lee Moore Hall) is a building on the University of Texas campus frequently used for improv rehearsals.
RLM's large lecture room on the ground floor near the escalators is the most preferable room for rehearsals, as it has a large stage area. If this room is occupied by another group rehearsing or some legitimate academic function, groups will usually default to a smaller lecture room upstairs, or any other open classroom with enough open space to rehearse in.
Though UT contains abundant open classrooms in many of its buildings on any given evening which could be surreptitiously used for rehearsal space, RLM is the only building which is usurped in this manner.
This tradition began when former Austin improvisor Andrea Young was a member of Girls Girls Girls while finishing her graduate studies in math at The University of Texas. GGG would rehearse there, then other troupes that Andrea was a member of.
Members of those troupes began to rehearse with their other troupes, until RLM became a somewhat reliable rehearsal space for many Austin improv troupes.