The property in meta tags allows you to specify values to property fields which come from a property library. The property library (RDFa format) is specified in the head tag.
For example, to use that code you would have to have something like this in your <head tag. <head xmlns:og="http://example.org/"> and inside the http://example.org/ there would be a specification for title (og:title).
The tag from your example was almost definitely from the Open Graph Protocol, the purpose is to specify structured information about your website for the use of Facebook (and possibly other search engines).