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.

This is any type of media, usually referencing images or video that can grow and shrink within the space available. This could also apply to a music/audio player. There are no set heights or widths, the media changes size as is appropriate on the page.

These containers have width set by percentages and not pixels or ems. They grow and shrink proportionally. This is why they are called fluid containers.