A case of some merchandise is a collection of items packaged together.
For consumer foodstuff such as canned goods, soda, cereal, and such, a case is typically 24 items, however cases may consist of any quantity depending on manufacturer packaging - cases are typically found in multiples of 4 or 6.
For larger bottles such as gallon jugs, a case is typically 4.
The term case binding in the book manufacturing industry refers to a collection of pages contained in a case which is attached to it.
The original case is often now called simply the binding, although the integrated manufacturing process still uses the term case to refer to the hard cover and spine.