APIs are like pre-made services that you can use on your apps, umm..., am I right?...What's are APIs in your mind?

Answer 1

An API has much more general meaning. It stands for "Application Programming Interface", and it formalizes the way how different pieces of software can communicate with each other.
Web-based API, for example REST (Representational State Transfer) protocol, is one commonly used way to build these interfaces between web applications. But it is not the only type of API by far.

https://www.freecodecamp.org/news/what-is-an-api-in-english-please-b880a3214a82/