1. One or more computer storage media storing computer-executable instructions for performing a method for identifying related strings for search query rewriting, the method comprising: accessing click log data; identifying session data for a user search query session in the accessed click log data, the session data including: a first user search query, a first set of search results provided for the first user search query, one or more additional search queries, and search results provided for the one or more additional search queries including a second set of search results provided for a first additional search query; determining that the first additional search query in the session data is related to the first user search query based on: (1) a similarity between the title or uniform resource locator (URL) of a web page included in the first set of search results and the title or URL of a web page included in the second set of search results exceeding a similarity threshold and (2) at least one of: (a) a comparison of dwell time between the first and second sets of search results, or (b) a comparison of a number of result links clicked on between the first and second sets of search results; in response to determining that the first additional search query is related to the first user search query, incorporating the first additional search query into a list of strings related to the first user search query; identifying one or more supplemental strings that are related to the first user search query, the supplemental strings including at least one of: the title or URL of a web page included in the search results provided for either the first search query or the first additional search query that was clicked on after the corresponding search results were provided, a snippet corresponding to a web page included in the search results provided for either the first user query or the first additional search query that was clicked on after the corresponding search results were provided, or a second user search query identified using random walk analysis such that the second user search query is identified when a URL included in the search results provided for the first user search query is clicked on and a similar URL included in the search results provided for the second user search query is also clicked on; incorporating the identified supplemental strings into the list of strings related to the first user search query; and from the list of strings, each string having at least one term, determining a probability of relatedness for a first term from a first string and a second term from a second string; receiving a search query submitted during a current session, wherein the search query includes the first term from the first string in the list of strings; and rewriting the search query based at least in part on the determined probability of relatedness for the first term and the second term from the second string in the list of strings.