C++: What is the difference between lvalue and rvalue references?

1int x = 10;
2int& lref = x;      // OK — lvalue reference
3int& lref2 = 10;    // Error — cannot bind lvalue ref to rvalue
4
5int&& rref = 10;    // OK — rvalue reference to temporary
6int&& rref2 = x;    // Error — cannot bind rvalue ref to lvalue
7int&& rref3 = std::move(x);  // OK — cast to rvalue
8
9void process(int& val) { std::cout << "lvalue\n"; }
10void process(int&& val) { std::cout << "rvalue\n"; }
11
12process(x);    // lvalue
13process(10);   // rvalue
14process(std::move(x));  // rvalue