[Karma Dorjee]

Data Extension(DE) are similar to table in DMBS database system, it has unique structure to hold different types of data.

Following are types of Data Extension:

1. Standard Data Extension
   1. Sendable Data Extension
   2. Non-Sendable Data Extension
   3. Testable Data Extension
   4. Template based Data Extension (Eg: Send log DE, Triggered Send DE)
2. Filter Data Extension
3. Random Data Extension

If your Marketing Cloud is connected with Salesforce org, you will Synchronised Data Extension (Salesforce_Contact, Saleaforce_lead), you cannot create this kind DE, this will be created by system while introducing the Salesforce Objects in Salesforce Marketing Cloud.

Also you night have noticed, Salesforce Data Extension, these DEs are derived from Salesforce objects or reports.