title: std::move() and xvalue in C++
body: <p>Can someone give me an "acyclic" definition/explanation of xvalue and std::move() behaviour? </p>
  
  <p>I looked on cppreference page, and it says "std::move() produces an xvalue". (Ok)</p>
  
  <p>Then I looked for "xvalue"'s definition and the first thing it says is it's a function call or overloaded operator expression, such as "std:move". (???)</p>