Put simply, a Data Extension is a table used to store

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What is a Data Extension?
information about your contacts. Think of them like individual spreadsheets of customer data stored in Marketing Cloud.

While subscriber lists use a single record to store every piece of information you have ever collected on a contact, with Data Extensions one person’s data can be split across multiple tables that are related to one another. The contact is linked across these tables using a unique piece of identifiable information, such as their email address.

For example, an ecommerce business, rather than trying to store absolutely every piece of their customer’s profile, purchase, and shipping information in subscriber list fields, may have different Data Extensions (tables of data) for:

Customer profile i.e. name, email address, country, birthday, etc.
Billing information i.e. payment method, transaction cambodia mobile numbernumber, purchase date, any promo code used, etc.
Shipping details i.e. shipping address, selected shipping method, shipping status.
Storing each of these data points in one list with hundreds of fields would create a hugely bloated database that’s difficult to work with!

With Data Extensions, the information is organised into separate tables that are related to each other. We call this a ‘relational database’. The same customer is identified in each Data Extension using a unique piece of information, known as a ‘primary key’ or ‘contact key’. This is usually an email address but it can be any data point of your choosing, so long as it’s unique to the contact.

Still a little confused? Hey, that’s normal.

Imagine your purse or wallet. Inside, you may carry a debit or credit card, a healthcare card, a library card, your driver’s license, and so on. Each of these cards contains different pieces of information about you; your membership number, credit card details, registered address, etc. The thing linking them all together is you. Loosely speaking, Data Extensions work in a similar way. Each card represents a table of data about you, making it quick and easy to access only the information you need, as and when you need it.

Types of Data Extensions
Some of the information you store about contacts in Data Extensions may not be required for your marketing activities. Billing information, for example, is required to process the payment and for accounting purposes, but it’s generally not used within marketing campaigns. For this reason, it’s possible to create two different types of Data Extensions in Marketing Cloud:

Sendable - can be used as a source for journeys in Journey Builder.
Non-sendable - cannot be used as a source for journeys but can be used for segmentation and personalisation within email campaigns.