@mew27 The naming convention is terrible for the value categories, there is a better categorization with a W shaped graph, but I can't quite find it right now...

This case though is pretty simple, lvalue is so your run of the mill variables (or function parameters), and a temporary is just a temporary, that's going to be destroyed before the next "statement". According to the language standard it's an insta-dangling reference and is forbidden. Like this:
int& x = 1;