When you use several windows simultaneously, only the front window is called Active Window. Only active window is effective for user's command.
"Focus" is a point at which application such as Excel, Word receive user's input.
On the whole blinking cursor has "Focus".
In Excel, active cell has "Focus".
Representative mouse pointers are as follow.
① Ordinary selection
② Selection of string
③Enlargement and reduction in horizontal direction
④Enlargement and reduction
⑤Selection of linked page etc.
It is important to distinguish the nature between "Focus" and "Mouse pointer". If you perform [mouse-right-click] at an ambient spot, the point you click turns out to be a position having "Focus".