CSS Flexbox, or the Flexible Box Layout, is a layout model in CSS that allows for the efficient arrangement of items within a container. It provides a way to distribute space and align items, even when their size is unknown or dynamic. This makes it easier to create responsive designs that adapt to different screen sizes. With Flexbox, you can control the direction, alignment, and spacing of items using simple properties. For example, you can easily center items both vertically and horizontally, or create equal spacing between them. This flexibility simplifies the process of building complex layouts compared to traditional CSS methods.