hours per week
"The constant value that Microsoft Project uses when calculating duration and work. Taking the default of 40 hours, a one-week task will be calculated as 40 hours and an assignment of 1 unit will calculate as 40 hours also. Changing the hours per week to 32 would retain the assigned work as 40 hours and therefore change the duration of the assignment to be 1.25 weeks. If the shift pattern for that week is unaltered (from the default 8 hours/day), the assignment (and task) will be complete at the end of that week and not within the next week. '
SOURCE; microsoft project glossary-projectlearning.net"