When we search a book in OPAC, if it checked out we can see the message "No items available". Many Koha users opined that this status message is awkward. We can use "No copies available" or something like. I think the message "No items available" more suitable for display the status of products in online shopping site. This is my personal opinion, lets discuss..
As a non native speaker, my understanding of 'item' is more generic than 'copy'.
I did a Google search on 'library item borrow' and 'library copy borrow' ('borrow' to filter out non librarian meanings of 'library'), and I found that the use of 'item' is the common use for libraries.
An other point would be that changing the wording for 'item' would have a huge impact on the whole Koha system, because 'item' is used everywhere.
Any other opinions?
If you need a different wording for "item" you could use separate translation files (.po files) for this variant, see discussion on IRC channel:
We did this for the Swiss spelling of the German language (de-CH)