16. A method comprising: under control of one or more processors configured with executable instructions, receiving a primary keyword and a request for retrieving related keywords corresponding to the primary keyword from a user; obtaining a plurality of related keywords corresponding to the primary keyword; grouping the plurality of related keywords into a plurality of groups of related keywords, at least one of the plurality of related keywords is included in each of the plurality of groups of related keywords and at least another one of the plurality of related keywords is included in a subset of less than all of the plurality of groups of related keywords; selecting a candidate group of related keywords from the plurality of groups of related keywords; and displaying related keywords of the candidate group to the user.
16. A method comprising: under control of one or more processors configured with executable instructions, receiving a primary keyword and a request for retrieving related keywords corresponding to the primary keyword from a user; obtaining a plurality of related keywords corresponding to the primary keyword; grouping the plurality of related keywords into a plurality of groups of related keywords, at least one of the plurality of related keywords is included in each of the plurality of groups of related keywords and at least another one of the plurality of related keywords is included in a subset of less than all of the plurality of groups of related keywords; selecting a candidate group of related keywords from the plurality of groups of related keywords; and displaying related keywords of the candidate group to the user. 17. The method as recited in claim 16 , further comprising: receiving multiple requests for retrieving related keywords corresponding to the primary keyword from the user; and updating and recording a frequency at which the multiple requests for retrieving related keywords corresponding to the primary keyword are received from the user, and wherein the selecting comprises selecting the candidate group of related keywords from the plurality of groups of related keywords based on the frequency of receiving the request corresponding to the primary keyword from the user.