mochila

As nouns the difference between backpack and mochila

is that 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 while mochila is (us|western us) a large leather flap that covers the saddle tree.

As a verb backpack

is to hike and camp overnight in backcountry with one's gear carried in a backpack.

As nouns the difference between bookbag and mochila

is that bookbag is a bag for holding books for school while mochila is (us|western us) a large leather flap that covers the saddle tree.