"edu" is one of the top-level domain names that can be used when choosing a domain name. It generally describes the entity owning the domain name as a four-year college or similar educational institution. (Educational institutions below four-year colleges are encouraged to use the geographic "us" top-level domain name.) Along with the second-level domain name (for example: "umich" in umich.edu), the top-level domain name is required in Web and e-mail addresses.
For more information, see gTLD (generic top-level domain name).