A knapsack, sometimes mounted on a light frame, but always supported by straps, worn on a person’s back for the purpose of carrying things, especially when hiking, or on a student's back when carrying books.

A similarly placed item containing a parachute or other life-support equipment.

(intransitive) To hike and camp overnight in backcountry with one's gear carried in a backpack.

(intransitive) To engage in low-cost, generally urban, travel with minimal luggage and frugal accommodation.

(transitive, rare) To place or carry (an item or items) in a backpack.