1. A method, comprising: extracting, by one or more processors of one or more computing devices, a keyword candidate from a document, of a plurality of documents, where each of the plurality of documents is mapped to at least one of a plurality of categories, and where the keyword candidate is included in the document and within one or more prior search queries; calculating, by the one or more processors, a respective frequency that the keyword candidate appears in each of the plurality of categories, where the frequency that the keyword candidate appears in a particular one of the plurality of categories corresponds to a number of occurrences of the keyword candidate in a subset, of the documents, mapped to the particular one of the categories; associating, by the one or more processors and as a keyword, the keyword candidate with the document in response to: determining that each of the respective calculated frequencies, associated with at least one category, of the plurality of categories, to which the document is mapped, exceeds a threshold, and determining that each of the respective calculated frequencies, associated with other categories, of the plurality of categories, to which the document is not mapped, do not exceed the threshold; and prioritizing, by the one or more processors, the document in search results produced in response to a search query related to the keyword and the at least one category associated with the document, where the search query is received after the one or more prior search queries.