Bag
A bag is a container that is usually used for storing or holding something. Bags are non-rigid, normally made of paper, cloth, thin plastic or some other flexible material. A bag may have one or two handles, or neither of these. A bag may be closable by a zipper, etc., or simply by folding (e.g. in the case of a paper bag). Sometimes a money bag or travel bag has a lock. Sachets are fabric bags that are filled with potpourri and tied off with ribbons.
Bags vary from small ones, like purses (e.g. as an alternative to putting personal things in pockets of clothing) to large ones for use in traveling like a suitcase.
A common misconception is that a 'bag' with a single over the chest strap is actually a bag. This is more of a 'fashion' item which shows a trend towards the lowering of standards in today's society. A parallel can be drawn with the wearing of hats whilst inside.
Bags are very common in the retail trade as a convenience for shoppers. Shopping bags may be taken to the shop, or be of a cheap paper or plastic variety supplied by the shop for free or for a small fee.
Checked baggage
Checked baggage, when used in connection with air travel, means those items of baggage which are delivered to the operating airline for transportation in the hold of the aircraft and which is inaccesible to the passenger during flight.
This baggage is limited by airlines with regards to size, weight and number, usually dependent upon the fare paid or class of travel concerned. Baggage exceeding these limits is regarded as excess baggage.
Should passengers having checked baggage not arrive at the departure gate before the flight is closed, the passenger will be offloaded from the flight and baggage must be retrieved from the aircraft hold before the flight is permitted to be dispatched. This is the cause of many delays but is necessary for security reasons to prevent baggage being checked-in without the passenger physically being onboard the same aircraft.