Hi Shareef,
Is it in Ariba or Oracle Apps? I guess unit_meas_lookup_code is a kind of chooser field for a user to select UOM (Unit of Measure like each, km etc) at PO line item level. You can define a list of UOMs to be used in your system. Most commonly used is each. At times, I have experienced lot of integration errors because a UOM (defined in source system) is not defined in target system. In such case, we are defaulting it to each to resolve any integration errors.
Best Regards,
Amit