It may sound like marketing wank, but it does a appear to be an established term of art in academia as far back as 1997 [1]

It just means that a person can't readily distinguish between the compressed image and the uncompressed image. Usually because it takes some aspect(s) of the human visual system into account.

[1] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C22&q=per...