Prerequisite: something required beforehand. In the case of knowledge, it is knowledge that is required to understand what is being taught. One part of that would be vocabulary. If you did not know the definition of prerequisite, then you would not know what I am writing about. If you were in a classroom where I was talking about the importance of prerequisite knowledge and did now its meaning, you would not know what I was talking about there either. Hopefully, you understand the importance of prerequisite knowledge.
I watch and listen to experienced professional educators teaching students. Sometimes they are middle school students and the teacher is presenting a lesson that a college student level. Is there any wonder why their students have a bewildered look on their face?
Knowledge is incremental. Do I have to explain that too? Figure it out.
I cringe when I see teachers overshooting their students. Is there any wonder why standardized test scores are declining?