An occupant is someone who lives or stays at a place for awhile. A lot of your junk mail is addressed "To occupant" because the sender doesn't know who lives at your address.
Being an occupant means you're occupying a place. This has nothing to do with owning a house or renting an apartment; if you live there, you're an occupant. There are other occupants too, as in politics. The President is often called "the current occupant of the White House," who replaced the former occupant. That kind of occupant has as much to do with politics as living space.