1. Computer-storage media having computer-executable instructions embodied thereon that, when executed, perform a method of determining a document score, which suggests a relevance of a document to a search query, the method comprising: receiving the search query comprised of one or more terms that represent a subject; identifying an equivalent subject that is semantically similar to the subject, wherein the subject and the equivalent subject comprise a subject group; and determining the document score of the document, wherein the document score is comprised of a subject-group score, and wherein the subject-group score is calculated using both a subject frequency, which includes a number of times the subject is found in the document, and an equivalent-subject frequency, which includes a number of times the equivalent-subject is found in the document.