Open Graph is a technology that provides information about a website or a website object. Among other things, this is how Facebook and G+ gets details about the youtube video that you just posted.
This plugin provides open graph headers for your idno site, and detailed descriptions for individual permalinks, but it also provides functionality to extract open graph details from other sites when you post links. This means that you’ll get some extra details displayed about a site when you post a link to it.
Hopefully this’ll be useful to you!