'backpack' definitions:

Definition of 'backpack'

noun

A bag carried by a strap on your back or shoulder [syn: backpack, back pack, knapsack, packsack, rucksack, haversack]

verb

Hike with a backpack; "Every summer they are backpacking in the Rockies" [syn: backpack, pack]

From: GCIDE

backpack \back"pack\ n. a bag carried on the back, supported by straps looped over the shoulders.
Syn: knapsack; rucksack; haversack. [WordNet 1.5]

From: GCIDE

backpack \back"pack\ v. i. to hike while carrying a backpack; -- often used in the form go backpacking; as, to backpack through the forest. [PJC]