ZLuC stands for the Zine Librarian (un)Conference. The first one was held in Seattle in 2009, and they have been held nearly every year ever since. There have also been mini-zine librarian unconferences held at the Olympia Zine Fest.
The zinelibrarians.info site has information about each event: Zine Librarian (un)Conferences.
Photo from the 2016 ZL(u)C held at Simmons College in Boston. Photo by Andrew Wang.