Application Programming Interface (API) can refer to the protocol specification that allows two applications to talk to each other, as well as an implementation that is conformant.

APIs specify how software components should interact with each other and defines the underlying functionality that is exposed to users. They are typically used to enable communication between different software programs, allowing them to exchange data and functionality with each other.

For example, a web-based application might use an API to access data or services from a third-party provider, such as a Web3 payment processing system.

APIs can also be used to allow different components of a larger system to communicate with each other, such as the interacting with different smart contracts to compose complex operations.