1. A system comprising: one or more computers; and a computer-readable medium coupled to the one or more computers having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations comprising: receiving an audio signal that corresponds to a spoken query term; performing speech recognition on the audio signal to select two or more textual, candidate transcriptions that match the spoken query term, and to establish a speech recognition confidence value for each candidate transcription; obtaining a search history for a user who spoke the spoken query term, wherein the search history references one or more past search queries that have been submitted by the user; generating one or more n-grams from each candidate transcription, wherein each n-gram is a subsequence of n phonemes, syllables, letters, characters, words or terms from a respective candidate transcription; determining, for each n-gram, a frequency with which the n-gram occurs in the past search queries, and a weighting value that is based on the respective frequency; generating, for each of the candidate transcriptions, a combined value based on combining the speech recognition confidence value for the candidate transcription with the weighting value for one or more of the n-grams that are generated from the candidate transcription; selecting an intended query term from among the candidate transcriptions based on the combined values; and causing a search engine to perform a search query that includes the intended query term.