Alt text, short for alternative text, is a descriptive text used to provide information about an image or graphic element on a webpage. It serves as a replacement for the image in case it cannot be displayed, and also helps visually impaired individuals understand the content of the image. Alt text should be concise, accurate, and relevant to the image it describes, making it an essential tool for web accessibility and search engine optimization. By including alt text, website creators can ensure that all users, regardless of their abilities, can fully engage with the visual content on their site.