Flexbox, or the Flexible Box Layout, is a CSS layout model designed to help create responsive web designs. It allows developers to arrange elements in a container efficiently, distributing space and aligning items even when their size is unknown or dynamic. This makes it easier to design layouts that adapt to different screen sizes and orientations. With Flexbox, items can be aligned horizontally or vertically, and their order can be changed without altering the HTML structure. It simplifies the process of creating complex layouts, such as centering elements or distributing space evenly, enhancing the overall user experience on websites.