What is a Distribution List?

A distribution list is a group of mail recipients that is addressed as a single recipient. Distribution lists are used to send email to groups of people without having to enter each recipient's individual address.

Where can I find them and what do they look like?

Address Book

You will notice that a distribution list has a group of people  beside the name, where a single email address has one person beside it.

Email to Line

In the email, you will see a this lets you know this is a grouping of email addresses.