Daypack
The term is often used interchangeably with backpacks. It is a smaller bag intended for everyday use. These are more compact and are ideal for work, school, or running errands. Reference image: Iswee Casual Daypack
A backpack is a spacious bag used for carrying all the things that you need. It has slightly more space than a day bag and is convenient for long trips. The term 'backpack' was first used in the United States in the early 1900s, even though there is evidence pointing to these being used in the early civilizations as close to 3300 BC.
A Bum Bag is also known as a Waist Bag or Fanny Pack and is worn around the waist. It can hold smaller objects and daily essentials. The bag portion of a Bum Bag is not detachable from the belt. It can be made from a wider variety of materials. Reference image: Prada Unisex Marsupio Belt Waist Bag