Knapsack/ˈnæpsæk/ Definition 1 of 2Pro Tip 1/3Outdoor Gear Knapsack is often used to refer to a bag for outdoor activities like hiking or camping. His knapsack was filled with trail maps and a compass. Pro Tip 2/3Casual Use The term knapsack is casual and commonly used in everyday speech, not just for specific gear. She grabbed her knapsack and keys before heading out. Pro Tip 3/3Size and Shape Knapsacks are generally smaller and lighter than large backpacks used for extended trips. I only need a small knapsack for my daily commute.