A backpack is a common item used for carrying various things such as books, clothes, and food. However, there are various other words that can be used to describe backpacks, depending on their shape, size, and function. A rucksack is a type of backpack that is often used for hiking or camping trips. A knapsack is a smaller backpack that is generally used for short trips. A daypack is a smaller backpack that is specifically designed for day trips and activities. A book bag is a backpack that is primarily used for carrying books. A pack is a general term used to describe any type of backpack or carrying device. Each of these synonyms can be used interchangeably to describe a backpack, depending on its specific purpose and style.