back·pack / ˈbakˌpak/ • n. a bag, often supported by a metal frame, with shoulder straps that allow it to be carried on someone's back. ∎ a knapsack used by students as a bookbag, or any small bag carried on the back. ∎ a load or piece of equipment carried on a person's back: a two-tank scuba backpack. • v. [intr.] [usu. as n.] (backpacking) travel or hike carrying one's belongings in a backpack: a week's backpacking in the Pyrenees he has backpacked around the world.DERIVATIVES: back·pack·er n.