Expandable divs and iframes - difference?

This may sound like a really stupid question but what is the difference?

they are completely unrelated.

Expandable divs make boxes expand, expandable iframes make iframes expand.
Magical, isn't it?

They're completely different, iframes is a frame of another page, divs are used to style your layout. As for expanding as the title says divs expand naturally without a height, on the other hand iframes need javascript to get the sources page height.