1. [ITS] A derogatory term for Unix, derived from Unix weenie. According to one noted ex-ITSer, it is “the operating system preferred by Unix Weenies: typified by poor modularity, poor reliability, hard file deletion, no file version numbers, case sensitivity everywhere, and users who believe that these are all advantages”. (Some ITS fans behave as though they believe Unix stole a future that rightfully belonged to them. See ITS, sense 2.)
2. [Brown University] A Unix-like OS developed for tutorial purposes at Brown University. See http://www.cs.brown.edu/courses/cs167/weenix.html. Named independently of the ITS usage.