First impressions are important.
My experience sofar indicates that just using “WIP” is better for conversations and softer buy in, but sometimes WIP is very tightly associated with “WIP Limit”, also WIP sounds very like WHIP!. So I have used “Work In Progress” (long hand) in conversations and it gets more doors open for continued conversation around team/process overload. Also just using “work in progress” is probably more in line with starting out with Kanban by showing what the current flow/phases are. One can also transition to “WIP Limit” later on when group is comfortable with concept.
Also I like Julia’s idea of using “level”, it’s softer, more transitionary and is like a half way house.