A flow from something (or somewhere) to something (or somewhere) else
"What percentage of claimant off-flows from jobseeker's allowance were due to the claimant claiming incapacity benefit?" http://www.parliament.the-stationery-office.co.uk/pa/cm200506/cmhansrd/vo050628/text/50628w28.htm
A channel or way by which surplus water can be discharged or allowed to flow off