This references the way the layout of the content of the page changes at specific breakpoints. For example, in our mobile sizes, usually our content lines up under each other for a one column layout. As the page gets wider, the content may shift to a two-column layout and so forth.
Quote:
The success of a site almost always hinges on its content. Content, as we are frequently reminded, is king. But if that’s the case, then navigation is the establishment that keeps him on the throne. — Aaron Gustafson