What is an "efficiency apartment"?

I've started early on my apartment hunting for November. And it's taken me five years of apartment living to finally google "efficiency apartment".

When you see the words "efficiency", it resembles the same feeling you get when you read the word "charming" or "cute" in an apartment ad. It means SMALL.

But according to the all knowing web:

An efficiency apartment is like a studio, except that is usually a little bigger and sometimes the bedroom is not part of the living room, it has it's own room.

So, eh, wouldn't that be considered a 1 Bedroom apartment (or 1BR in craigslist lingo)?

Well, yeah that's why they came up with a creative word for it "efficiency". AKA, really, really small one bedroom apartment or a big no-bedroom apartment.

So there you have it.