Hugo partials are reusable template fragments — the building blocks of a maintainable Hugo theme. Any piece of HTML that appears in more than one place belongs in a partial: site headers, footers, navigation menus, article cards, SEO meta tags, social sharing blocks, author bios. Once defined, a partial is called with a single line from any template. This guide covers the full range of how partials work and patterns that make them practical for a publishing site.