What math are you reading? All of the math textbooks I’ve read, in university, begin each section with a precise definition and then proceed to examine the implications. Theorems begin with a precise statement of the hypotheses and conclusion before proceeding to the proof.

If you’re trying to read math on Wikipedia, without having studied it, you’re going to have a bad time. Wikipedia’s math pages are better used as a reference to remind you of what you already know and give you a jumping-off point for related topics. They are not meant to teach you math.