The repository policy characterises pre-prints as being the version of the paper before peer-review and post-prints as being the version of the paper after peer-review, with revisions having been made.
This means that in terms of content, post-prints are the articles as published. However, in terms of appearance this might not be the same as the published article, as publishers often reserve for themselves their own arrangement of type-setting and formatting. Typically, this means that the author cannot use the publisher-generated PDF, but must make their own PDF version for submission to a repository.
For more information on this particular definition of 'pre-print' and 'post-print' visit Sherpa/Romeo. Sherpa/Romeo is a project that collects information from publishers regarding their policies in relation to open access repositories. In order to maintain consistency, VU uses the definition of 'pre-print' and 'post-print' as described by Sherpa.