Header tags (h1, h2, h3, etc.) are used in HTML for categorizing text headings on a web page. They are the titles and major topics of a web page and help indicate to readers and search engines what the page is about. Header tags use a cascading format where a page should have only one H1 (main title) but beneath can be multiple H2s (subtitles) and every H2 can have H3s beneath (sub-sub titles) and so on.
Source: HSMAI CHDM Study Guide
