A book bag is a durable bag, satchel

Satchel (bag)

A satchel is a bag, often with a strap. The strap is often worn so that it diagonally crosses the body, with the bag hanging on the opposite hip, rather than hanging directly down from the shoulder. They are tradionally used for carrying books....

, or backpack

Backpack

A backpack is, in its simplest form, a cloth sack carried on one's back and secured with two straps that go over the shoulders, but there can be exceptions...

 that is used to carry book

Book

A book is a set or collection of written, printed, illustrated, or blank sheets, made of hot lava, paper, parchment, or other materials, usually fastened together to hinge at one side. A single sheet within a book is called a leaf or leaflet, and each side of a leaf is called a page...

s and sometimes other supplies such as notebooks, ring binder

Ring binder

Ring binders are folders in which punched pieces of paper may be held by means of clamps running through the holes in the paper...

s, and file folders, particularly by student

Student

A student is a learner, or someone who attends an educational institution. In some nations, the English term is reserved for those who attend university, while a schoolchild under the age of eighteen is called a pupil in English...

s. Typical designs include backpacks, hand-carried briefcase

Briefcase

A briefcase is a narrow box-shaped bag or case used mainly for carrying papers and other documents and equipped with a handle. Lawyers commonly use briefcases to carry briefs to present to a court, hence the name...

s, bags with drawstring

Drawstring

A drawstring is a string, cord, or rope used to "draw" or tie closed an opening in fabric or other material...

 closures that can be hand-carried or worn over one shoulder

Shoulder

The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...

, and messenger bags that are typically worn over one shoulder.