- link tag for relation between document and the canonical url
- PageMaps: invisible blocks of XML that add metadata to pages.
- Microformats: tags used to mark up visible page content along predefined types.
- RDFa: an alternate standard for marking up visible page content along arbitrary types.
- Microdata: a new HTML5 standard for marking up visible page content.
- Page Date: features on a page indicating its date
Protocol / Vocabulary
- Schema.org - Google
- Open Graph (Tag|Protocol) - Ogp - Facebook
Social Media
Social media uses metadata also to style the card that are used to embed link to a website.Example:Test / Validator
Documentation / Reference