HTML 5 microdata: making content machine-readable for web design

Microdata has been a particular focus area of the HTML 5 development. Essentially, microdata ( is a meta data ) that allows designers to create annotations for content in formats that are  machine-readable.

Microdata contains name-value pairs grouped together and dubbed "items".  Microdata items  have properties that provide definition to the elements they surround.

Five of the most common metadata formats:

• Itemscope - Declares that an item is a microdata element and states that all child elements are components of the microdata format
• Itemtype - Defines the vocabulary to be used by the microdata format.
• Itemprop - A data element
• Itemid - A unique identifier of an item
• Itemref - Can reference another element on a web page using an id

Example of usage in HTML:
The following is an example usage of itemscope. In this example, all the child elements of <p> are part of the itemscope meta data.

<p itemscope itemtype="">Content goes in here</p>

Microdata can be nested to provide context. It can also create associations using common information formats--for example, group first name and last name into the annotation of a person's name:

<span itemprop="name">Tony Hawke</span>

Search engines already use the meta data or microdata of web pages to provide more context for the content of sites they crawl and rank. Google for instance already supports the following information types:

• reviews
• events
• people profiles
• products
• business listings

SOURCE:
https://www.w3.org/TR/html5/microdata.html