1.  A pack or knapsack, often of canvas or nylon, to be carried on one’s back, sometimes supported on a lightweight metal frame strapped to the body.
2.  A piece of equipment designed to be used while being carried on the back.
verb (used without object)
3.  To go on a hike, using a backpack: We went backpacking in the Adirondacks.
4.  To place or carry in a backpack or on one’s back.