Checked baggage (also referred to as cargo baggage) is stored and transported in the aircraft cargo hold.
This category is generally comprised of larger (and, usually, heavier) items such as bigger suitcases, sports equipment, oversized items, musical instruments, and just about anything else that air carriers allow to transport on a passenger airplane, but is unfit to be brought into the cabin of the aircraft.
As the term suggests, checked baggage will have to be handed to the airport staff when you check in for your flight and will be inaccessible to you for the duration of the flight. This is why careful and thoughtful planning when packing can save you a lot of trouble during your travel. For example, if there are medications or documents that you need to have access to at all times throughout your trip, then it is best to have those in your carry-on baggage.
Please, do take a moment to review the baggage policy of the air carriers on your itinerary to learn about the permitted count, size, and weight for every type of item you would like to bring on the trip.