By structured data we mean that information is marked-up (with code) to signal what it is about. Information that is obviously a name to you and I (humans) but isn’t so obvious to the search engines. Structure data originally started out as something called microformats with simple structures for information so that developers could signal to the search engines what words specifically meant, i.e. a name, a phone number – like a vcard for a contact and an hcard for a calendar entry event.
Coding like this is easy to get slightly wrong so a testing tool is essential to make sure you’ve done it right. The smallest mistake can render the entire effort a waste of time. I know!
Up until now the only way to test structured data on your web pages with Google on the Rich Snippets Testing Tool. A great tool itself which has been upgraded only a month or two ago.
If you want to learn about microformats I recommend taking a look at the Schema.org website.
At Matter Solutions we’ve used it mostly to denote organisations and events and is seems pretty clear that the structured Review is a big part of how Google places (now in Google+) picks up reviews from external sources and recognises those citations.
Any questions? Comment below and we’ll be happy to help.