This is an Abhidhamma term, which means “the knowledge of distinguishing between mind and body”.
It relies on the strictly Abhidhamma interpretation of nāmarūpa as “mind and body,” which is not found in the suttas at all.
Warning: using the Abhidhamma to understand the suttas will only lead to weariness and vexation! You will have to learn a bunch of complicated stuff, and then spend years unlearning it! Like I did! 