I'm looking at various grid systems to make a responsive design, but I keep coming across the same thing that puzzles me : What's a *row* in a design where everything can move based on the screen size ?

Say I want the following design on a large screen :

![enter image description here][1]

Which turns into that on a mobile screen :

![enter image description here][2]

What would a "row" be in that site's html ?


  [1]: https://i.sstatic.net/HhTyp.jpg
  [2]: https://i.sstatic.net/oQIhk.jpg