So Id never heard of this before my previous company, but the fact that others have even heard of it tells me this is an actual thing across the US workforce/industry/etc.
Like so many other companies, this company distributes payroll every 2 weeks (every other friday). Therefore, the pay periods are of course, every 2 wks. So here's the breakdown. Of course, a 2 wk pay period consists of 10 business days. Generally it's expected that you work 8 hrs/day 5 days/wk for a total of 40 hrs/wk. Standard stuff. Now ppl at that company are given the choice of whether or not they wanna opt into this 9/80 schedule. So the 9/80 comes in as having those employees work NINE hours per day on Monday through Thursday. The first friday of the pay period is a standard 8 hour day. Now that you've spent 2 wks working four 9hr days, youve banked up 8 hours, right? Great! So that alternate friday you now have off work. So out of 10 business days in each 2 wk period, you only have to work 9 of those business days. It sounds like a significant amount of extra work on Mon-Thurs, but when you get it done, one hour is really not even noticeable.
Crappy salary structure notwithstanding, this was one of my favorite things about this job. Even having one weekday off every 2 wks makes a HUGE difference in the work/life balance. TALK TO YOUR HR DEPT ABOUT THIS!!! Every company should be doing this. Or at least those who are able to at all.