This is indicated on the right hand side of your ticket. Economy class passengers generally are allowed 20 kg, except British Airways who permit 23KG. Travelling to the USA Business Class is around 30-35 kg. First is up to 40 kg. Hand luggage remains pretty much generic: one piece per passenger, restricted in size (esp. short haul flights), and up to 8kg in weight. For larger items such a s windsurfers etc. you should check with the tour operator or airline with whom you have booked. Some additional charges may occur.
That amount of baggage, generally consisting of the passenger's personal effects, carried by the airline and cruise line free of charge.
The maximum number of bags that you are allowed. Midwest airlines permits a maximum of three checked bags and no carry-on bag, or two checked bags and a maximum of one carry-on.