An API -Application Programming Interface- is a set of specifications that applications can use to communicate with each other. To put it very simply, APIs - in this case Athento's - allow us to access the document manager's functionality from another application.
For example, suppose we need to display a document in an application of ours - which has nothing to do with Athento - but the document is stored in Athento. In that case, our application could call an Athento URL or web service that will return the preview of the document.
Just as users use Athento's user interface to use its functionality, software applications use the APIs for the same.
The consumption of the APIs means the use of Athento and even if there are no users directly using the product interface, there is a use of the application. In many occasions, this consumption even requires special infrastructure needs.
For this reason, Athento's plans include limits to the use of the API.