Just because you understand something and make use of it regularly, doesn't mean it's easy to explain it to someone else. I wrote explanations of the following programming concepts: API, Client/Server Pattern, DOM, HTTP/TCP/IP, JSON, MVC, SQL, Binary Number, Boolean Logic, Data Structures, OOP, Operating Systems, Recursion, Git and Version Control, CLI.
It took longer than expected. The goal was to write clear, to-the-point explanations that provide high level context and answer the 'why' question before diving into the details.
I decided to also hand-draw illustrations. It was hard work to do this writing, but it was also fun :)