When I checked at the national parks out west it's the whole rigs length, TV and trailer. Does seem kind of odd though, I've got a 20' trailer and need a 40' site, which is usually the biggest.
From what I read here many ignore it and just go by their trailer size without issue.
Happy Motoring
Bob & Deb
W Ma.
12 F150 HD SCAB EcoBoost LB 4x4
14 Escape 5.0 TA