What's the difference between variable definition and declaration in JavaScript?

Question

Is this a variable definition or declaration? And why?

var x;

..and is the memory reserved for x after this st

Answer 1

var x, y, z;

var x;

var h = 4;

i = 4;

all the above are global variables if placed at the top, (outside any functions)

Lets say that the javascript has a function start

function start() {
      x = 5*5;
}

the global variable x is now equal to 25

Where as if the var x; was not placed outside of any functions, that variable x would just be local to that function.