> when every seat is full and there's already very little seat-to-seat distance, the aisle is crammed with people face to back with nothing to hang on to, and the vestibules are all full to the point that people are standing with nothing to support them if the train brakes hard, that is a crammed train.

That was the Metra BN line in Chicago when I lived there, at least the rush hour departures at around 5:00pm. I was on a train so full that I could not even fully get into the vestibule, I had to push people in with my body so the door could close behind me. Many times the CTA trains were similarly full.