One aspect of Search Engine Optimization (SEO) is to positively influence the ranking of web pages. Search engines rely partially on the meta information your web pages provide.

Meta information has a number of forms. Most important are the title of the page and the meta tags for adding semantic information.

There are standards for names of meta tags. HTML pages commonly use

• the title element
• meta elements with
  
  • description
  • keywords

There are additional meta tag names defined by other standards. One of them is Dublin Core.

The Dublin Core Schema is a small set of vocabulary terms that can be used to describe web resources (video, images, web pages, etc.), as well as physical resources such as books or CDs, and objects like artworks. 

Wikipedia

Here is an example for an HTML fragment with information derived from the document's properties:

<link rel="profile" href="http://dublincore.org/documents/dcq-html/">
<link rel="schema.DC" href="http://purl.org/dc/elements/1.1/">
<meta name="DC.title" content="My Title">
<meta name="DC.description" content="My short description for the page.">
<meta name="DC.subject" content="one, two, three">

While meta tags may or may not be used by search engines for indexing, the title and descriptions are typically used to display the results. And the information is available for other consumers as well. Everyone with access to the web page has also access to the meta data.