25. The non-transitory computer-readable medium of claim 21 , wherein matching the source web page document with the item comprises matching the source web page document with the item using a biasing factor.
21. A non-transitory computer-readable medium storing program code operable to cause one or more computers to perform operations comprising: receiving a source web page document; identifying, by a preprocessor based on formatting information of the source web page document, a plurality of regions contained within the source webpage document, that would be displayed to a user visiting said source web page document, wherein the regions contained within the source webpage document contain content between opening and closing HTML or XML tags; determining at least one local concept expressed in each previously identified region, wherein determining the at least one local concept comprises identifying words in the document and aligning the words with concepts, wherein said at least one local concept expressed in the previously identified region is expressed by two or more words in the region; determining a score for a local concept expressed in each previously-identified region, wherein the score is based on a size of, or an importance associated with, the previously-identified region; analyzing the previously determined at least one local concept of each region to identify and eliminate from consideration one or more local concepts that are unrelated to local concepts of other of said previously identified regions by creating a ranked global list of all of said local concepts; analyzing the previously identified regions to identify and eliminate from consideration one or more regions that are unrelated to regions by comparing a ranked list of local concepts for each of said previously identified regions to said global list; determining a source meaning for the source web page document, wherein the source meaning for the source web page document is a weighted vector of said previously determined local concepts expressed in the source web page document that remain after the eliminations; and matching the source web page document with an item selected from a set of items by comparing the previously determined source meaning and a meaning of the item.