The versions of a work allowed for self-archiving are specific to the work.
For published journal articles, it can be the pre-print, post-print and/or published version. You may check the SHERPA-RoMEO website: http://www.sherpa.ac.uk/romeo/ to see which version is allowed and if any embargo is imposed. Alternatively, you may check publishers’ websites directly for more details on their self-archiving policy for specific journals.
The definitions of the versions are below:
For other published works, check the copyright transfer agreement that you signed with the publisher for the versions allowed for self-archiving.
For works which you did not sign any copyright transfer agreement, you retain the rights (unless the funding agency of the research that resulted in the work stipulates otherwise) and can decide on the version to archive.