Google has published an improved help center which gives information on advanced search operators such as "link:":
Google supports several advanced operators, which are query words that have special meaning to Google. Typically these operators modify the search in some way, or even tell Google to do a totally different type of search. For instance, "link:" is a special operator, and the query [link:www.google.com] doesn't do a normal search but instead finds all web pages that have links to www.google.com.
This is helpful if you do day-to-day SEO analysis. Read full article: Advanced Google Search Operators