In web development, a slug refers to the part of a URL that uniquely identifies a specific page on a website in a human-readable format. Typically, it's the end part of the URL that explains the page’s content, like ‘about-us’ or ‘contact-form’. Slugs are created to provide a user-friendly and SEO-friendly website navigation experience. They are important for optimizing a website's structure and content for search engines, making it easier for users to understand and remember URLs, and enhancing the overall accessibility of a website.