Wikipedia:Google Test

• as a quick and rough to check that something actually exists (we get articles about things that don't... personal theories, personal fictions etc) See the Check your fiction policy for more.

  Q. What is the minimum number of matches you should see if the term is not made up? ( 3, 27, 81 )? A couple hundred perhaps!

  A. That depends on the article's point of view. If narrow, fewer references are required. Try to categorize the point of view, ( whether it is NPOV, or other) eg: notice the difference between Ontology (philosophy) and Ontology (computer science).

• as a quick and rough check for copyright. When a new or IP user submits a large chunk of text, it's a good idea to be mildly suspicious and "Google test" a few 10-word or so segments.

It should be stressed that neither of these applications is conclusive evidence, but simply a first-pass heuristic.