12. 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: accessing audio data; accessing information that indicates a first context, the first context comprising a first physical environment or physical state of a device that records the audio data; accessing at least one term; accessing information that indicates a second context, the second context comprising a second physical environment or physical state associated with the accessed term; determining a similarity score that indicates a degree of similarity between the first physical environment or physical state and the second physical environment or physical state; adjusting a language model based on the accessed term and the determined similarity score to generate an adjusted language model, wherein the adjusted language model includes the accessed term and a weighting value assigned to the accessed term based on the similarity score; and performing speech recognition on the audio data using the adjusted language model to select one or more candidate transcriptions for a portion of the audio data.
12. 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: accessing audio data; accessing information that indicates a first context, the first context comprising a first physical environment or physical state of a device that records the audio data; accessing at least one term; accessing information that indicates a second context, the second context comprising a second physical environment or physical state associated with the accessed term; determining a similarity score that indicates a degree of similarity between the first physical environment or physical state and the second physical environment or physical state; adjusting a language model based on the accessed term and the determined similarity score to generate an adjusted language model, wherein the adjusted language model includes the accessed term and a weighting value assigned to the accessed term based on the similarity score; and performing speech recognition on the audio data using the adjusted language model to select one or more candidate transcriptions for a portion of the audio data. 28. The system of claim 12 , wherein: accessing information that indicates the first context comprises accessing information that indicates a first geographic location of the device that records the audio data when the audio data is recorded; accessing information that indicates the second context comprises accessing information that indicates a second geographic location associated with the accessed term; and determining the similarity score comprises determining a similarity score that indicates a degree of similarity between the first geographic location and the second geographic location.