Microdata

Microdata is a specification to embed machine-readable data in HTML documents. Microdata consists of name-value pairs (known as items) defined according to a vocabulary. Schema.org provides a collection of commonly used markup vocabularies.

The basic syntax includes the itemscope attribute to define an item and the itemprop attribute to describe one of the item's properties. Specify types using the itemtype attribute, which can take values defined in your vocabulary of choice. For example, schema.org defines types such as http://schema.org/Person or http://schema.org/PostalAddress.

The following example (from Wikipedia) shows how to use microdata to describe a person:

<section itemscope itemtype="http://schema.org/Person">
  Hello, my name is
  <span itemprop="name">John Doe</span>,
  I am a
  <span itemprop="jobTitle">Graduate research assistant</span>
  at the
  <span itemprop="affiliation">University of Dreams</span>
  My friends call me
  <span itemprop="additionalName">Johnny</span>
  You can visit my homepage at
  <a href="https://www.example.com" itemprop="url">www.example.com</a>
  <section itemprop="address" itemscope itemtype="http://schema.org/PostalAddress">
    I live at
    <span itemprop="streetAddress">1234 Peach Drive</span>
    <span itemprop="addressLocality">Warner Robins</span>
    <span itemprop="addressRegion">Georgia</span>.
  </section>
</section>

See Test Your Schemas to debug your markup and validate it against the supported schema.