About bootstrap's well

Does div have any real meanings itself? I used to think div is just like a tag, which can make the code looks more clear.
I thought if put the “well” right behind the “row”, I should get the same answer, which is not. Does the div take its own space?

use div class=row well
instead of
div class=row
div class=well

A div is a blank element, but it’s default display is a block element. Other than that, there are very few preset appearances and behaviors. relative positioning too.

Div is just a “division” so you can group logical elements together (for easy placement, or styling).

Nothing magical about Bootstrap “well”. It just adds a rounded 1px border around a div, and gives it a gradient background and some slight drop shadow.