Excess Baggage is the luggage that exceeds the airline's allowable limit for weight
or number of pieces. Passengers are usually charged extra for excess baggage,
if excess baggage is permitted at all.
Other definition:
Excess Baggage is the luggage that exceeds an airline's weight allowance and is liable to an extra charge.
The Travel-Glossary: Everything about Travelling, Sightseeing and the World.