Unclear error message "partially moved value"...

[MatejLach]

Consider the following code:

fn main() {
    let x = box 5i;
    let y = x;
    println!("{}", *x);
}

This yields error: use of partially moved value: *x.
What exactly is a "partially moved value"?
I think that a value should either be moved, or not be moved.
Perhaps a cleaner message could be:
"x" is no longer a valid pointer, did you mean "y"? or something along these lines.