o·ver·draft 
(ōvər-drăft′)
(ōvər-drăft′)n.
1.
a. The act of overdrawing a bank account.
b. Abbr. OD or o/d The amount overdrawn.
c. The maximum amount of credit extended to a customer.
2. also o·ver·draught (-drăft′)
a. A current of air made to pass over the ignited fuel in a furnace.
b. A series of flues in a brick kiln designed to force air down from the top.
c. The air so forced.