Hi Sanjay,
Creation ind. B means that the PReq's are created by MRP, i.e. not directly from the prod. order. Hence these PReq's don't carry the order no.
MRP checks the overall demand/supply situation in the plant and creates PReq's for missing qties; i.e. these PReq's only indirectly can be assigned to production orders (demand).
BR
Raf