You’ll find these terms ‘strange’ when you are just starting your Arch journey (even if using Arch downstream distros like Manjaro) but you’ll come across them in various forum discussion and wiki references.
This tutorial quickly explains the different kinds of repos Arch Linux offers and how you can enable them. It also answers the question: why bother about these repos in the first place?
The tutorial also touches on the Chaotic-AUR repo. I’ve actually taken the plunge and started using the Chaotic-AUR yesterday. So far, so good.