1. A computer implemented method of associating advertisements with a displayed web page, said method comprising the steps of: a) (i) obtaining advertisement keyword meanings associated with said advertisements, each of the advertisement keyword meanings comprising a specific intended meaning of a word contained in the respective advertisement; (ii) indexing the advertisements according to the associated keyword meanings; (iii) storing said indexed advertisements in a database; and b) (i) disambiguating content of said displayed page to identify keyword meanings of words contained in said displayed page, each of said page keyword meanings comprising a specific deduced intended meaning of a respective word on the web page, in view of the context of its usage on the web page; (ii) expanding said page keyword meanings using their relevant semantic relations to other word meanings to create a list of expanded page keyword meanings; and, (iii) searching said database of indexed advertisements to identify matches between the expanded page keyword meanings and the advertisement keyword meanings; (iv) extracting advertisements indexed to the advertisement keyword meanings matched to the page keyword meanings, said extracted advertisements comprising advertisements relevant to said displayed page; (v) displaying said relevant advertisements in association with the displayed page.