A distribution list is a list of email addresses, either in a standard email program (e.g., Microsoft Outlook) or on a server system (e.g., Active Directory). A user can send an email to the distribution list, which automatically distributes the email to all the email addresses on that list. This makes managing a list of recipients easier by not have to select or type in each email address every time an email needs to be sent to all those recipients.
Depending on the need for the distribution list, it could have as few as two email addresses in it or as many as a hundred or even a thousand addresses, as many as needed. There is virtually no limit to how many email address it could contain.