CSS masking is a technique in web design that allows designers to partially or fully hide parts of visual elements such as images, videos, or SVGs by using another graphical element as an alpha or luminance mask. This method streamlines the design process by eliminating the need for complex software like Photoshop and enables more dynamic and interactive web designs. The CSS specification includes various masking properties and sub-properties, such as mask-image, mask-repeat, and mask-type, which allow for extensive customization and styling options. While CSS masking can enhance visual appeal, it also presents challenges in terms of browser compatibility and accessibility, requiring thoughtful integration of performance and accessibility best practices. The guide further explores the application of CSS masking in real-world scenarios, such as animating text and hiding content, and emphasizes the importance of ensuring accessibility by using proper alpha channels and color contrast.