When someone says “API is a set,” they are likely referring to the fact that an API (Application Programming Interface) is essentially a set of rules, protocols, and tools that developers use to build software applications. This set of rules allows developers to access and interact with the functionality of a particular software system or service in a structured and standardized way, without needing to understand the underlying code or architecture. In other words, an API defines the way in which different software components can communicate and work together.