The language surrounding the publication process can get confusing.  The NISO/ALPSP Journal Article Versions (JAV) Technical Working Group's recommendations, NISO RP-8-2008, provide a standard for describing the versions of scholarly journal articles. The recommendations define seven stages for journal articles:
Author's Original (AO): The original version of the article submitted by the author.
Submitted Manuscript Under Review (SMUR): The version of the article under review. This version is equivalent to what has been commonly known as the pre-print.
Accepted Manuscript (AM): The version of the article that has been accepted for publication. This version is equivalent to what has been commonly known as the post-print. 
Proof (P): The proof version of the article
Version of Record (VoR): The final published version of the article. This is also known as the "publisher version". 
Corrected Version of Record (CVoR): A corrected version of the final published version
Enhanced Version of Record (EVoR): An enhanced version of the final published version Below are the standard terms for different versions of an article throughout the publication process. 

Thanks to the OSU Open Access Policy passed by the Faculty Senate in 2013, faculty at OSU may self-archive any version of their article that precedes the VoR immediately to ScholarsArchive@OSU. 

Researchers should consider the following questions before posting their work online.

1. Who owns the copyright to your work?

You establish copyright when you put your work in a "tangible form," which can be as simple as an email.  Copyright is actually a bundle of rights.  Copyright holders have the exclusive right to reproduce, distribute, display, perform, and create derivative works.  It is common for authors to transfer their copyright to publishers, but I encourage you to retain copyright if at all possible.  If you transfer your copyright to a publisher, it may make it more difficult to distribute your work later, or even to use your own work for teaching and new research.  One way you can do this is through an addendum that modifies the publishers' agreement in order to allow you to keep key rights for distribution.  SPARC provides addenda and information about how to use them.

2. If the publisher holds the copyright, do they allow you to distribute a version?

Publishers often let authors archive the pre-print or post-print version of an article (see sidebar) online, usually after an embargo period of one to five years.  You can use SHERPA RoMEO to determine what version you can legally distribute.

3. What are the terms and conditions for sharing your work on a particular site?

Take a moment to find out what permission you're giving a site when you upload your work and "click through" the terms and conditions.  ScholarsArchive@OSU, for example, requests a distribution license that allows OSU Libraries to reproduce, translate, and distribute your work worldwide in print and electronic format (a non-exclusive, irrevocable license).  It does not affect the copyright of your work.  Other sites may request permission to use and distribute your work in different ways.  If you sign an exclusive license, it may limit what you can do with your work elsewhere, even if you retain copyright.

The Library often receives variations of the two following questions:

"How did my article end up on that website?"

"Am I legally liable if someone uploads an illicit copy of my article to a website?"

Just because something is posted online doesn't mean it's not infringing copyright.  The effectiveness of copyright law has been challenged in the digital age.  Neither internet service providers (such as Facebook, Youtube, or ResearchGate) nor copyright holders have the ability to scour and police the millions of content items uploaded and shared each minute.  If Youtube were responsible for monitoring every video for copyright compliance, it would be out of business.  Congress responded to this problem by passing the Digital Millennium Copyright Act (DMCA)*, which set up a new system that gives Online Service Providers (Academia.edu, Youtube, ResearchGate, Google, etc.) "safe harbors" from monetary liability based on the behavior of "third parties" - usually site users uploading content. In return, Service Providers must provide an easy way for copyright holders to challenge content with a takedown notice.  Academia.edu and other sites have received takedown notices from Elsevier and other publishers.  If you or someone else uploads content for which you don't hold copyright, the most likely response from the copyright holder is a takedown notice.

*One major piece of the DMCA, less relevant here, makes it illegal to circumvent technical protection measures.  This has had a negative effect on the cryptography research community.