[ahi]

It gets much much more complicated than that. There are never ending discussions about FRBR: Functional Requirements for Bibliographic Records. https://www.ifla.org/references/best-practice-for-national-b...

* Work is defined as the intellectual or artistic content of a distinct creation. It refers to a very abstract idea of a creation e.g. Shakespeare’s Romeo and Juliet and not a specific expression.

* Expression is the intellectual or artistic realization of a work. The realization may take the form of text, sound, image, object, movement, etc., or any combination of such forms.

* Manifestation is the embodiment of an expression of a work. For example a particular edition of a book or a specific music recording.

* Item is a single exemplar of a manifestation. Cataloguing is generally done, based on an item directly available to a cataloguer