It’s neither. Unless you’re 1099/hourly or in sales you get paid to be available to work during a set period of time (generally not specific hours), regardless of how much you accomplish during that time. Keep in mind this works both ways - if you finish your work in 5 hours and spend the next 3 messing around on Reddit or whatever you still get paid for 8. Getting paid for actual hours worked isn’t as much fun as you probably think.