What is API?
In layman's terms, an API is an agreement between two people stating: "If you give me this instruction, I will perform this action, or return this information"
OR
An application programming interface (API) is a particular set of rules ('code') and specifications that software programs can follow to communicate with each other. It serves as an interface between different software programs and facilitates their interaction, similar to the way the user interface facilitates interaction between humans and computers.