Sources represent sources of customer and billing data for your ChartMogul account.
Sources represent systems that your customers and billing data originate from. For example Stripe, Recurly, but also custom sources such as a manual API-based integration. The API only allows one to create custom sources, though other integrations may be added through the ChartMogul UI.
Historically, sources were named "data sources". While this name change isn't reflected everywhere, they refer to the same thing. Additionally, some endpoints still use data_source as parameters or returned properties for the sake of avoiding breaking changes.