What's an index?

So meandering from link to link filling our brain cells with snippets of ideas which we may not have an urgent need for at the moment, but enrich our web of associations may be passe, but we still use online indexes, don't we? Apparently not. Finding information via a search engine has become so simple, that we hardly ever take the opportunity to seek out organized knowledge via an index. Years ago I encountered teachers who didn't know the difference between a search engine and an index, and it seems to have only become worse since then.

Go to: Surfing for information?, or
Go to: How to lose an online argument.