An email 'alias' is an email address and it can contain different email address.  If someone sends email to this alias, all the email addresses under this alias will receive the emails.

E.g.: There are 10 staff in sales department, each is with an individual email address marked as sales1-sales10@urdomain.com. The sales team set up an alias of salesteam@urdomain.com for this department and include all 10 staff's email address in this alias. In this case, if anyone sends an email to salesteam@urdomain.com, all 10 staff will receive an individual email with the same content in their own email box.