11. A system comprising: a memory to store instructions; and a processor to execute the instructions to: receive a first document that includes a plurality of advertisements; identify one or more advertisements, of the plurality of advertisements, that have been selected more than any other advertisements of the plurality of advertisements; retrieve particular documents associated with the one or more advertisements; extract concepts from the retrieved particular documents, at least one extracted concept of the extracted concepts being associated with anchor text associated with a link in one of the retrieved particular documents; and associate the extracted concepts with the first document.
11. A system comprising: a memory to store instructions; and a processor to execute the instructions to: receive a first document that includes a plurality of advertisements; identify one or more advertisements, of the plurality of advertisements, that have been selected more than any other advertisements of the plurality of advertisements; retrieve particular documents associated with the one or more advertisements; extract concepts from the retrieved particular documents, at least one extracted concept of the extracted concepts being associated with anchor text associated with a link in one of the retrieved particular documents; and associate the extracted concepts with the first document. 12. The system of claim 11 , where, when extracting the concepts from the retrieved particular documents, the processor is to: analyze textual content of the retrieved particular documents, and associate the textual content with the at least one extracted concept.