What does App::class mean? The class cannot be found.

Question

  function bind($abstract, $concrete = null)
    {
        return Container::getInstance()->bind($abstract, $concrete);
    }

App::class What does it mean? That class cannot be found

Answer 1

  function app(string $name = '', array $args = [], bool $newInstance = false)    
  {      
    return Container::getInstance()->make($name ?: App::class, $args, $newInstance);   
   }

The code is posted wrong