Should be the seat tube length being described, though not all sellers are sophisticated enough to understand this.

In actuality, what has changed more than the relative proportions of bike tube lengths (which were more a function of which company built them than anything else), is the philosophy of bicycle frame fitting. 30 years ago, if you had an inch of standover, and a "fistful" of seatpost showing, that was considered generally accurate frame fitting. Today, three or four fistfuls of seatpost is considered "normal".