What does header tag mean?

earlier days its for formatting header or title text. Now these days its functioning more when we talk of SEO. these are the tags search engine's favorite.
so use it properly. put important text relevant on you site.

Header tags are very important today as far as SEO is concerned.If used properly it helps search engines to crawl your pages regularly and hence increases traffic. Use the header tags to give a proper heading to your page based on the keyword analysis...

The <h1> tag is very important for seo google looks at this to see what the main topic of the page is also the title and keywords should match

-Graham

head tags are googlebot friendly.

The H tags are heading tags that format your text into headings we mean this family of HTML tags: Headings reflect the document structure much in the same way you'd do an outline. H1, H2, H3, H4, H5, H6. They define a Web page's structure much like an outline displays the structure of a term paper or technical document, you need to mind the content of each heading tag, it's probably a good idea because these are structural tags, HTTP headers are something else entirely, I decided not to confuse the situation further by bringing them up, they're important to both Web site accessibility and search engine promotion. What he is essentially saying is that the search engines look to these tags for relevant meaning for SEO.