The MID is a unique number assigned to a merchant’s account to identify the merchant throughout transaction processing. The MID is designated by the acquirer or processor. The merchant account uses the MID to identify the merchant, a Terminal Identification Numbers (TID) to identify each of the merchant’s terminals, locations or facilities and a Gateway Identification Number (GID) to identify the particular network gateway to which the transactions will be routed.
A merchant may have more than one MID if the merchant is engaged in two different types of transactions that card association regulations do not allow to be mixed. A automotive repair shop that also rents cars would have two different MIDs as the car rentals would be a separate merchant category code than the repair business.« Back to Glossary Index