The term Application Programming Interface (API) is a specification of protocols, procedures, and services that can be used as building blocks by a programmer to implement a required functionality. An API may represent a web-based system, operating system, database system, computer hardware, or software library.
In addition to that, in everyday life, the term API is often applied to the system that implements the specification. For example, you might be familiar with Twitter APIs (https://developer.twitter.com/en/docs) or Amazon APIs (https://developer.amazon.com/services-and-apis), or you might have worked with devices (sensors) that are able to respond to a request by providing the data (measurement results). So, when programmers say we can use an Amazon API, they mean not only the description of the provided procedures, but the services themselves.
In Java...
