Data Sources let you create and maintain data sets for use in Screens. Examples of these are a list of choices, a product catalog or a list of contacts.
You can use Data Sources in Choices questions across any number of your Forms. Data Sources are also used as the backing data for other Screen types. As an example, you could have a Contacts data source which you expose as a "Listing" type screen. This would have its own icon on your app start screen.
Data Sources save time by centralizing your data sets in one place. They also automatically update any changes you make to any Screens to which the Data Source links. The platform will ensure that mobile app deployments of these linked Screens will also seamlessly update.
If you have any technical personnel, you can even update your Data Sources through the integration API (see these articles for more information). This opens up the ability to integrate with your existing systems. Changes to database tables or lists within your existing systems automatically update into your mobile app. For example, you may have a catalog of products that you maintain in your inventory software. By hooking up the integration API, any inventory changes could automatically flow to your app users in the field.