hCard is a simple, open format for publishing people, companies, organizations on the web, using a 1:1 representation of vCard (RFC2426) properties and values in HTML. hCard is one of several open microformat standards suitable for embedding data in HTML/HTML5, and Atom/RSS/XHTML or other XML.

How is it related to vCards?

The vCard standard (RFC2426), has been broadly interoperably implemented (e.g. Apple's "Address Book" application built into MacOSX).

In addition, many bloggers identify themselves by name and discuss their friends and family. With just a tad bit of structure (as defined by hCard), people can discuss others in their sites in such a way that spiders and other aggregators can retrieve this information, automatically convert them to vCards, and use them in any vCard application or service.

This specification introduces the hCard format, which uses a 1:1 representation of the properties and values of the aforementioned vCard standard, in semantic HTML. Website owners can both embed hCards directly in their web pages, and style them with CSS to make them appear as desired. In addition, hCard enables applications to retrieve information directly from web pages without having to reference a separate file.

Source: Microformats.org