What does Co-op mean?

Co ops are a really weird thing that seem to only exist in New York anymore. It's kind of like owning a condo; except instead of owning the "land" in the case of owning the condo, you own shares (your apartment) in a corporation that is the building. Essentially, to live in a coop, you have to be approved both financially and personally by the other "shareholders" of the building --i.e. the other people in the building scrutinize everything about you. It's pretty dumb; but, a lot of the older, nice buildings, particularly uptown, are still in the coop regime.