Backpacking is packing (carrying) all that you need to survive (usually for a few days, but sometimes for months) on your back. Done for pleasure, usually in beautiful places. It is a form of walking or hiking wherein the traveler carries a pack that contains food, water, and shelter or the means to obtain them, for a trip that includes one to several overnight stays.
Overnight stays may be out of doors (under the stars, in a tent, or under some sort of permanent shelter such as in a hostel.