A case of some merchandise is a collection of items packaged together. A case is not a strict unit of measure. For consumer foodstuff such as canned goods, soda, cereal, and such, a case is typically 24 items, however cases may range from 12 to 36, typically in multiples of six. 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. (There are also cases for books e.g. slipcases which merely enclose a book.) 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.