OOP
Out of production
When an item is no longer being made, it may be classified as "out of production" or "OOP." Most people see it when looking for collectible items or spare parts for old assemblies.
There are various reasons an item may go out of production. Instances include when an item is not selling well, or only a certain number of the items were intended to be produced.
Typically, items that are OOP increase in value because there is a limited number available. As a result, these items often become collectibles, making the OOP acronym more common in the collecting community. Examples of collectibles include sports trading cards, coins, comic books, cars, and toys.
Disc golf disc manufacturers also commonly use the acronym to describe discs that are no longer produced. Reasons the discs have gone OOP include when a manufacturer goes out of business or phases out a disc mold for a new style.
Example
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A book, record, or video game that is OOP is "out of print" - meaning no more copies are currently being made. You're most likely to encounter this acronym on online sales and auction sites, in listings for out-of-print items.
For example, a listing for the first edition of Batman: The Long Halloween may begin "1st edition Batman: The Long Halloween collection - OOP." OOP books and other items often fetch a high price, as they are rare and HTF.