Well yes it was online in that sense, which was great. But what I meant to point out was that the complete MSDN help library came shipped on two CDs that you could locally install. It was really really good. There was a description, detailed background info, and usually at least a few example code snippets using the function. I was later a astonished at how sparse and useless documentation for many other libraries/languages was compared to that, especially when it came to example usage. Some notable disappointments included e.g. the Java/JDK docs (v1.4) and the early Android docs (v1), which both required looking at the code because the docs were severely lacking (both have improved by now).

I think you can still download the whole MSDN help library for offline use, but I don't believe that nowadays that would be enough for daily work use. Lots of useful info and example use is scattered around blog posts and StackOverflow answers now, instead of being a part of the documentation itself.