ATG - ankles to glutes is a polite way, a$$ to grass is another, it basically means a deep squat like you see in olympic lifting.
Parallel means that if you draw a line from the crease of your hip to the top of your knee, that line would be parallel to the ground. So it isn't thigh parallel to ground really (unless you can see the femur with your xray vision), nor does it mean anything with respect to how your lower legs relate to your torso, unless by accident.
In the hole - if you have a heavy barbell and you squat deep and you have to start back up to standing - what it means to be "in the hole" will be self-evident
Below you see a book cover with a proper parallel squat in the middle, a toddler squatting atg naturally and an oly lifter in the bottom of an overhead squat - essentially atg
