It is a professional representation of your email address that uses your first name and last name. For example, John Doe's current email address is email@example.com. With first.last, John's email alias could be firstname.lastname@example.org. It is also a more definitive way of identifying yourself to another colleague where they might know your first and last name, but not your eight character email name. This is an optional service being offered to faculty and staff.
This article is part of the FAQ on first.last email aliases