What is the difference between luggage and carryon?

Each airline may have a slightly different rule as to exactly what size. Best thing is to check with the airline. In order to keep the passenger compartment uncluttered and safe, the airlines place rules and size limits on the luggage that each traveler can carry on the plane. The primary rule is the size limit stating that bags carried on board must be small enough to store below your seat or in the overhead compartment. Currently the basic rule is that carry on baggage must be no taller than 22 inches, no wider than 14 inches, and no deeper than 9 inches. In many cases, you'll also have to contend with limits on weight. Below are some particular airline rules. as I said you should get the list when purchasing tickets or prior to because these rules are subject to change.

Luggage is what you check in when you arrive at the airport. Once you check it in you can't take it on the plane with you as it will be stored in the luggage hold. As for carry on that is a smaller bag that you can take on the plane with you, usually you carry your personal and more precious items in there such as your passport, money, laptop etc. You can keep this on the plane with you while you fly. Hope this helps!

Any luggage you bring onto the plane is considered carry on, but not all carry ons are luggage. Duffle bags are fine to use as long as it's within your airline's carry on allowance. Check your airline's website for allowances.

Uh...duh, one is to put your travel items in. The other is just gross: http://en.wikipedia.org/wiki/Carrion