Good question, with answers ranging from "a bunch of hand-edited HTML files" to "a set of HTML files generated from a non-HTML syntax such as a markdown derivat

Good question, with answers ranging from "a bunch of hand-edited HTML files" to "a set of HTML files generated from a non-HTML syntax such as a markdown derivative or a programming language's object-literal syntax", with the latter (static site generators) being quite different from the former. And then there's also SGML which has everything HTML, as a last-mile markup language for delivery to browsers, assumed to have available for authors, such as text macros and shared fragments for eg. menus, auto-generating document outlines for page navigation, processing markdown into HTML, filtering into RSS or SERPs, etc., and even moderately complex dynamic site features such as integrating external/syndicated content and screening/validating user comments for malicious or other undesired input such as script, broken comments, external/spam links, and the like.