An Email alias is an additional Email address attached to your POP3 Mailbox.
For instance, you could set up an alias to use for your hobbies or interests such as FootballMadDad@uko2.co.uk. This would be associated with Dad@uko2.co.uk.
Or ProfessorMum@uko2.co.uk could be an alias to Mum@uko2.co.uk.
Any emails sent to any alias of an address will all go to the same mailbox.