In the US, we also say "on the floor." For example, a nurse might say, "I work on a medical-surgical floor." The difference between "unit" and "floor" in the US is that "unit" implies more specialized care with less patients per nurse. For example, we talk about being in a "burn unit" or "intensive care unit" while we might say "neurological floor" "post-op floor", etc. I hope this helps.