A catalogue is an organized list of items, often with descriptions. Libraries use catalogues to help people find books: you can search the catalogue by title, author, or subject to discover where a book sits on the shelf. Museums maintain catalogues of their collections, describing each painting, sculpture, or artifact they own. Companies send catalogues showing products they sell, complete with pictures and prices.

A true catalogue is systematic and detailed, with items organized according to clear principles. When scientists catalogue newly discovered species, they carefully record each one's characteristics and habitat. When you catalogue your baseball card collection, you're creating an organized record of what you have.

The word can also be a verb. If your teacher asks you to catalogue the problems with a proposed solution, she wants you to list them methodically, one after another. The American spelling is catalog, but both versions mean the same thing. Whether it's a seed catalogue showing every variety of tomato available or a library catalogue tracking thousands of books, the purpose remains the same: helping people find exactly what they're looking for in an organized, searchable way.