Linguistically, there should be the different property or feature between cheeks and the parts right near them for us to call cheeks “cheeks.” What is the main difference between cheeks and the other parts right near the cheeks? I mean, how do we distinguish cheeks and the other parts?
"Cheek" isn't really a biology specific word with a specific definition within the field, it's more of an everyday expression. Vis-a-vis Grey's Anatomy 3rd Edition doesn't even use the word at all.
In fish, for example it's mainly defined as the space between important features which have a defined function (eye and front edge of operculum).
Even the Cambridge dictionary defines it by (mostly) what it's in-between:
the soft part of your face that is below your eye and between your mouth and ear:
So definitions seem to be fairly consistently that the cheek is defined by its spatial relation to other features, rather than a "thing". Loosely speaking, this would be reification (treating something abstract as a physical thing), and it's quite commonplace.