Which tag is used to define the largest header in HTML?

The tag used to define the largest header in HTML is <h1>. This tag is significant because it denotes the most important heading on a page, which helps both in organizing content hierarchically and in improving search engine optimization (SEO). The <h1> tag is typically used for the main title of the document, and screen readers often emphasize this tag, making it critical for accessibility.

Using headers in descending order from <h1> to <h6> signifies a structure where <h1> is the most important, followed by <h2>, <h3>, and so on, with <h6> representing the least important heading. The <header> tag, on the other hand, is an HTML5 element that represents a container for introductory content or navigational links but does not define a header level like the heading tags do. This distinction is important as it highlights the role of headers in creating a logical flow and hierarchy within a webpage's content.