Web Applications Stack Exchange is a question and answer site for power users of web applications. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

In Google, if you use the search term "define:mathematics" it will provide you with definitions of the word mathematics.

How does Google determine which pages on the web are definitions for that word? (e.g. are the meta tags that you can add to a page to say that this page is a definition page?)

share|improve this question
up vote 3 down vote accepted

*EDIT: And looking further, it seems someone else has identified other sources so maybe my hypothesis doesn't hold. That article gives much better insight than I do. (The page is also 4 years old, but the most relevant post I could find.)

Doing a few random searches, it looks like all the answers come from the same sets of sources. My educated guess would be that Google has already determined sources which are trustworthy/reliable and have written algorithms to parse/search these resources and return these results in an order which is consistent with its other search algorithms.

I base this hypothesis on that I haven't seen any sources outside of these specific ones in approx 10 different searches:

  • en.wikipedia.org/wiki/
  • wordnetweb.princeton.edu/
  • en.wiktionary.org/

This page offers some addditional suggestions on how to properly identify definitions in your HTML however the no conclusion was reach on how Google sources these definitions.

share|improve this answer
you beat me to it! – warren Aug 2 '10 at 19:33
depends on what you search - I did a couple searches and found other citations, such as biz.uiowa.edu/iem/trmanual/IEMManual_4.html I'd imagine they don't add it manually, as it's just a manual from a college website, but it's easy to see how it got interpreted as a dictionary, since the heading is 'Glossary.' – eds Aug 2 '10 at 19:36
I noticed that, too, after further investigation. See my edit. – Michael Aug 2 '10 at 19:37
I get a 403 Forbidden when accessing this link webmasterworld.com/google/4113436.htm that you posted? – Guy Aug 2 '10 at 20:11
It just loaded fine for me. :) Try accessing through a proxy? – Michael Aug 2 '10 at 20:14

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.