The Magento API (Application Programming Interface) allows third-party applications to interact with your Magento instance programmatically. This is the way the application communicates and exchanges information with Magento. The Magento API is language-independent so it does not matter what programming language a developer uses, he/she can connect to Magento through the API. It provides the ability to manage Magento stores by making simple calls. These calls enable working with the number of Magento features such as customers, catalog, sales orders, inventory, checkout operations, and many more.
Magento gives an opportunity to select which API to use - SOAP/XML-RPC or REST - each of which will fit the developer's preference.