Online vs. On-Line
http://user-assistance.blogspot.com/2009/06/online-vs-on-line.html

Hughes, Michael A.
User Assistance
2009

Abstract:

This isn't a discussion of hyphenated vs. not hyphenated. It examines the difference between putting a PDF file on the Internet (what I call an on-line document) and having a truly electronic Web presence for that content (what I call an online document). Unfortunately, the two often get bundled together.