Data Extensions are tables made up of many different field types. Salesforce uses data Extension as the repository or list of emails to send targeted emails from. An email address is known as the subscriber key. It is a unique identifier that is used to identify individuals in your lists.
Data Extension stores subscriber and any other types of data. It can also be used to maintain subscriber information which cannot be stored with profile or preference attributes in subscriber lists as well as to store imported data from external systems.
