[unfocused]

I'll try and explain it simply with no technical information.

An API, or Application Programming Interface, allows you to interact with software using pre-defined agreements, or contracts.

Think of API as a set of legal contracts. I use this analogy when explaining it to lawyers.

If I give you $5, and I say give me an Apple, you will give me an Apple, as expected by the predefined contract, that I receive an Apple.

If I end up receiving Broccoli, then what we have here, is a bug. Or, in other words, the contract has been broken.

Now apply this to other domains in commerce - e.g. I give an ID of an item in a store, and I get back the name of the item, it's price, and if it's stock.