I'd say that a "corporation" is a "large business" that has offices in more than one country and is traded on an exchange/has investors in some other way.

Probably best answered by the poster, though.

I guess I was trying to imply a huge business with suits and cube farms and offices around the world... think an international bank or similar.

I would ask directly, then. For example "How many people work in your company?" or "In how many countries does your employer have offices?"

I would answer "who knows" to both of those things ('s not like i'm in HR) but I'd still be able to get a sense of whether I was working at a business or a corporation from the culture.

Thats a good description, thats what I was really going for.