The std::move() operator is a cast that gets an xvalue reference to an object, allowing it to be moved. Moving the object instead of copying it increases efficiency.

For example, consider the following swap() function:

template <typename T>
void swap(T& a, T& b)
{
    T tmp(a);
    a = b;
    b = tmp;
}

When this runs, a is first copied to tmp, then b is copied to a, and finally tmp is copied to b. If a and b were expensive objects to copy, this would be very inefficient.

With move(), we can rewrite the swap() function this way:

#include <utility>
template <typename T>
void swap(T& a, T& b)
{
    T tmp(std::move(a));
    a = std::move(b);   
    b = std::move(tmp);
}

Now if a and b are of a class that has a move constructor and assignment operator, they will be efficiently moved rather than copied.