With a single Gmail email address, you can create an unlimited number of alias accounts to help sort and track incoming mail. Your email aliases can be created either by adding dots to your address or by tacking on a “+” phrase. For example, if your email address is email@example.com, you can also use firstname.lastname@example.org or email@example.com, and so on. The plus used after your name can be used to track mail from specific sources. For example firstname.lastname@example.org could be used when requesting information from “somesite.com.” For more, read these articles from Consuming Experience or MakeUseOf.