CSS, short for Cascading Style Sheets, is a language used to describe the presentation and styling of a document written in HTML or XML. It provides a way to control the visual appearance of web pages, allowing designers to specify how elements should be displayed on the screen, printed, or spoken.

With CSS, you can define various aspects of a webpage’s appearance, such as colors, fonts, layouts, and animations. It works by associating specific styles or properties with HTML elements or classes, enabling the separation of content and design.