I think there are two types of lists in Sharepoint. Internal lists and external lists. External lists means when we create any list by any of the templates like announcements, calender,Custom list etc. Then what are the internal lists in sharepont. Correct me if I am wrong.
External list refers to Lists that have an external data source. http://msdn.microsoft.com/en-us/library/ee558778
And the internal list is a normal list in SharePoint.