Colloquially if most people eat there, you have to ask a server for a bag its a restaurant, if its normal or at least not noteworthy to walk out (or drive thru) with a bag of food its a store. One is primarily a place to eat, and they also happen to sell food. The other is a place to get food, although you can often sit there and eat.

Internally if its a franchise most call it a store (Hi we're store #35135 and our computer is broken ...). My source is my sister who worked a long time ago at McD. So the first "site" museum is called store number 1, her job title eventually was "store manager", their annual economic results are reported as "same store sales" etc.

(Only responding because you were downvoted.) I also would not generally call "fast food" "restaurants". When I read the title, I was thinking "huh, what ads? ones at the restaurant itself? the ludicrous websites restaurants tend to? but aren't those usually only showing shots of the interior and not the food?" and then I realized "oh, they mean fast food". I certainly eat at places like Subway and Taco Bell all too often, but it sounds wrong to me (in the cultural linguistic context that I have) to then say "I went to a restaurant today", I'd have to say "I got fast food" or something.

You might have been downvoted by others, but you're right in that it _is_ a cultural point. A burger, for example, does not count as proper meal for most people above 45 in my home country (Central/Eastern Europe). And for them, a proper meal must start with a soup. :)

For me, restaurant is a place where food is important.