If something is slipcased, it means it has a protective covering that can be slipped on and off, like a book in a special cover.
Slipcased things are usually special or important, like a fancy book or a valuable gift.
Examples:
The slipcased book is very pretty.
I want to buy the slipcased edition of the movie.
The slipcased album is on the top shelf.
I keep my special toys in a slipcased box.
In the museum, there is a slipcased statue made of gold.
The slipcased phone is very expensive.