The acronym CSS stands for Cascading Style Sheets. It is a style sheet language used in web design to control the presentation and layout of HTML documents. CSS enhances the aesthetic aspect of web pages by enabling developers to apply styles such as fonts, colors, spacing, and positioning. This separation of content (HTML) and style (CSS) allows for greater flexibility and easier maintenance. By utilizing CSS, developers can create responsive and visually appealing designs that adapt to different screens and devices.