The page refers to both the content and the HTML source code of a page that can be optimized, as opposed to off-page SEO, which refers to links and other external signals. On-page SEO (also known as “on-site SEO”) is the practice of optimizing website content for search engines and users. Common on-page SEO practices include optimizing title tags, content, internal links and URLs. On-page SEO (also called on-site SEO) is the practice of optimizing web pages to rank higher in search engines.
It includes optimizations for visible content and HTML source code.