RNTP vs GRNTP

Can anyone tell me what exactly is the difference between RNTP and GRNTP? In the data dictionary RNTP is "monthly rent" and GRNTP is "Gross rent (monthly amount)". The values in the data are different from each other, with (from what I've looked at) GRNTP being larger, so I'm guessing that GRNTP may have something other than rent included?

Thanks,

John Grumbine