An email alias is an additional email address (name) that you can assign to an existing email account.

For instance, if your account name is "jdoe", then your email account will automatically receive any email sent to jdoe@yourdomain.com (where yourdomain.com is your actual domain name).

You might wish for people to be able to send email to you at john@yourdomain.com as well. Using an email alias, you can do this without having to set up additional accounts within your email program (for instance Outlook).