The additional variable introduced in an unbalanced transportation problem to equalize supply and demand is known as a "dummy variable" or "dummy source/destination."

In an unbalanced transportation problem:

• If total supply exceeds total demand, a dummy destination is added with a demand equal to the excess supply. This allows any unused supply to be "transported" to the dummy destination, ensuring that all supply values are utilized in the optimization process.
• If total demand exceeds total supply, a dummy source is added with a supply equal to the excess demand, ensuring that all demand values are met.

The transportation cost associated with transporting to or from this dummy source/destination is usually set to zero, as this movement does not correspond to a real shipment but rather balances the transportation model mathematically.