Backpack vs. Rucksack vs. Knapsack - Picvalue CorpWe live in a world where manufacturers use the terms backpack and rucksack interchangeably,so you can have a hard time understanding this, especially when you buy such bags online and can't see and inspect them in person. To make it easier for you, we've created a guide for choosing the right backpack size when shopping online.It will give you a starting point to make an informed choice.