backpack \back"pack\ n. a bag carried on the back, supported by straps looped over the shoulders.
Syn: knapsack; rucksack; haversack. [WordNet 1.5]
Source: The Collaborative International Dictionary of English v.0.48
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]
backpack
Source: WordNet (r) 2.0