How do you define riding levels (english riders)?

To me it is no experience, beginner, advanced beginner, intermediate, and advanced, and there is no one scale you can go by. And I'm not going to make one either. At a summer camp you may be advanced while at a competitive hunter-jumper school you may be beginner. If your looking for a horse and you aren't sure what level they are (for example if it says "no beginners please." well obviously your not a beginner but that could mean a lot of things) then call the owners and ask.