Keep asking yourself who's the intended reader for this? For instance, if you're writing chapter 5 of a series, then you can reasonably assume the reader would be well-versed in content entries from previous four chapters of the same series. No need to repeat any concept already covered in first four chapters preceding that. However, if the content is not something a reader is supposed to know, it's best if you explain in 2-3 sentences. Make the content as beginner friendly as possible, without compromising quality. To that end, use examples to illustrate a concept. Or, use diagrams (tools like Excalidraw can help with this), or tables, or even images or videos. Beginner friendly coverage of concepts are comprehensive. If you write a specific concept once, so anyone who didn't understand that before can now grasp it reading that content - it benefits every other contributor out there. Because they can simply refer to that in their writing, without having to covering same concept.