Explain HTML5 Semantic Tags in details.

HTML5 semantic tags are elements that clearly describe their meaning in a human and machine-readable way. They provide information about the type of content they contain and the role they play in the webpage structure. Here are some of the most commonly used HTML5 semantic tags:

1. <header>: This tag is used to contain introductory content or a set of navigational links. A <header> element typically contains the section’s heading (an h1-h6 element or an hgroup element), but can also contain other content such as a table of contents, a search form, or any relevant logos.

2. <nav>: This tag is used to wrap major navigation blocks in the document, such as the primary site navigation. It can be used multiple times on a page for different sets of navigation links.

3. <main>: This tag is used to specify the main content of a document. The content inside the <main> tag should be unique to the document and should not appear elsewhere on the site. It should be unique to the document, excluding content that is repeated across a set of documents such as site navigation links, header or footer information.

4. <article>: This tag represents a self-contained composition in a document, page, application, or site, which is intended to be independently distributable or reusable. This could be a forum post, a magazine or newspaper article, a blog entry, or any other independent item of content.

5. <section>: This tag represents a standalone section of a document, which could have its own heading. It is a broad scope that can be used for grouping together thematically-related content.

6. <aside>: This tag is used to represent a section of a page that consists of content that is tangentially related to the content around it, and which could be considered separate from that content. It can be used for sidebars, pull quotes, or for advertising, for example.

7. <footer>: This tag is used to contain information about the author, copyright information, and links to related documents.

8. <figure> and <figcaption>: The <figure> tag is used to mark up diagrams, illustrations, photos, and code listings, along with a caption, while <figcaption> is used to provide a caption to the <figure>.

These semantic tags not only make the code easier to read for developers, but they also provide important context to search engines and assistive technologies like screen readers, improving accessibility and SEO.