France Touring 2 - Aires and Aires
As Bognormike says, there are different sorts of Aires ( it just means "area").
So, Motorway Services are called "Aires", but amongst the ones with filling stations, cafés etc, are tiny ones with just a bunch of picnic tables and a loo. They might well have a Campervan sign, but that just means you can empty your cassette etc there, and obviously park up if you like.
Neither of these are recommended for overnighting, but especially not the picnic table / loo variety.
The Aires we all use and love are Aires de Camping Cars, which are carparks of various sorts, designated by the municipality for our use, or provided by a campervan shop, supermarket etc., some with facilities, some without, some free, others not.
It is more complex than that, I hope that gives the gist of it.
Helen