As a noun backpack
is 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 [[carry|carrying books.
As a verb backpack
is to hike and camp overnight in backcountry with one's gear carried in a backpack.
As an adverb cat is
how much.
As an adjective cat is
how much.