So it refers to the amount of pages that contain that keyword or which is optimized for that keyword?
The amount of pages deemed relevant to the query, for that particular search.
the "estimate" differs from what you see if you go to Google and actually type in the keyword and do the search
That's a separate topic with prior discussion in the Google forum [webmasterworld.com] - there's no authoritative number of results for a query: it depends on factors like location, the details of the query and which data is accessed to determine the result.
[edited by: Receptional_Andy at 10:52 pm (utc) on July 8, 2008]
GeeKumar - I think you might be confusing the Google Suggest numbers with those from the Adwords Keyword tool [webmasterworld.com] which does indeed show estimated search volume. Google Suggest gives numbers of results.