ELI5: Explain Like I'm 5

Application programming interface

An application programming interface, or API, is like a toolbox full of different tools. Whenever you use a phone or a computer, you're using an API. An API helps make sure that different pieces of software can work together. It's like if you had a bunch of Legos and wanted to make a model. The API is like the instructions that show you how to put the pieces together.