Saks is a real chain. The original branch is located on Fifth Avenue in NYC, hence the name. There are many Saks Fifth Avenue and Saks Off 5th stores nationwide.
Yes, Saks fifth Avenue is a real store. It's a department store (like Macys or JC Penny's) but high end and very expensive. The original store is in NYC on 5th avenue where the store gets its name.
It sure is! It's not a store that is in a mall, it's in New York City on Fifth Avenue and the name of the store is Saks. I've been in that store many times.