What is a heading tag? H1, H2, H3 tags?
Heading tags (H1, H2, H3 etc.) are HTML markup used to organize and designate the most important parts of a single web page. Think of them collectively as an outline that helps Googlebot determine what your page is all about.
Traditionally, the H1 tag was used once per page, as close to the top as possible, to designate the main theme of a document. It was once a critical on-page SEO element with a decent amount of influence on rankings. In recent years, however, much of that influence has been reduced but their use is still important.
The H2 tags are used to break up specific sections of the main theme and can be used several times as needed. H3s, and up are less important but still can be used to designate important parts within each section.
In 2017, heading tags can be used in a variety of ways depending on how your page is presented. The emergence of HTML5 changed the game, making multiple H1 tags make sense.