Breakpoint

A breakpoint is a screen width at which your layout reconfigures itself. Below it the page looks one way; above it, another. It is the hinge that makes responsive design work.

For example, a three-column layout on a wide monitor might collapse to a single stacked column once the screen narrows past a certain breakpoint. You choose these widths based on where your content starts to break down, not on specific devices, since there are too many phones and screens to target individually.

The behavior is handled in CSS.