API is an application programming interface, which describes how programs interact with each other.
The description of the interaction usually includes the functionality of the program, but it does not reveal the essence of the whole process, i.e. the API remains a simple tool for the user.
All API components are strictly ranked, and high-ranked elements take information from low-ranked ones for their work.
Examples of the use of API are registration in applications using social network accounts, prompt receipt of certain data from the corporate API (e.g., weather forecasts), the ability to view videos from YouTube on other resources.