What is Apples “NeuralHash” exactly?

From what I can tell, Apple's CSAM scans iCloud uploads with its local database reports the hits to iCloud. If iCloud see's 30 hits or so, Apple manually reviews it. [1]

What isn't clear is the "NueralHash". Is this just a perceptual hash they have renamed? If so, I wonder how they created these since the NCMEC database isn't perceptual hashes. Does that mean they accessed the original content to create their "NeuralHash" database?

[1] https://www.youtube.com/watch?v=OQUO1DSwYN0