What is a "professional camera"

A lot of concert (and other) venues note that no "professional cameras" are allowed, and by extension, that "non-professional" cameras are okay. This post isn't intended to cover whether one has the right, or not, to take pictures at a concert (or how to do so respectfully/discretely). Instead, I just wish that someone would define what a professional camera is...

• Does "professional" mean that one is making money from their pictures; e.g., like a professional vs. amateur athlete? If so, then it's the use of the images, and not the type of camera that defines "professional."
• Or does "professional" mean interchangeable lenses? This doesn't make much sense either, since by this logic the $2800 Sony RX1R and $1300 Fuji X100s are non-professional, while the $500 Nikon D3200 or 1-system are professional?
• Does "professional" mean a zoom lens? Telephoto? A certain length?

Here's a list of camera regulations at each of the NBA arenas. Some of policies actually have a useful level of specificity! In addition to detachable lenses, the length of the lens seems to be a determining factor (6" seems to be the cutoff between non-professional and professional cameras).

The Fuji X-system (specifically thd X-E1 and similar) should be okay by most, but not all, definitions. It's not a DSLR, it has a relatively low-profile (i.e., no big viewfinder hump), and most of the lenses are under 6". The only sticking point is that it does have a detachable lens.

I've never been hassled with my X-Pro1 (or now X-E1, since it's even smaller) with the 60mm f/2.4 lens. I just received the 56mm f/1.2 which is bigger than the 60mm, but hopeful still won't garner much notice.

Update: I did recently get hassled by someone checking bags at a concert over my X-E1 wearing the 56mm lens. I mildly protested, and another person working the doors came over and after asking if it was a "zoom lens" (which it isn't), let me in. In the future, I should make sure the X-E1 is wearing a pancake lens when getting checked at the door so that it resembles a point and shoot, which they seem to be fine with.