Baggage Allowance is the set of rules regarding Customer luggage and established by the airline, such as luggage size, number of bags, weight, etc., that do not impose additional charges to the passengers.
Exceeding these limits set off additional costs to the travelers.
Other definition:
Baggage allowance indicated on the right hand side of your ticket. Economy class passengers generally are allowed 20kg for checked luggage. Travelling to the USA Business Class is around 30-35kg. First Class tends to be up to 40kg. Hand luggage remains pretty much generic: one piece per passenger, restricted in size (especially for short haul flights), and up to 8kg in weight. For larger items such, as windsurfs or bicycles, you should check with the tour operator or airline with which you have booked. Additional charges may occur.