This means that they have an alternate title. One example of that would be on Lee Childs list:
The 4th book in the Jack Reacher series was called Running Blind in North America, but The Visitor in the United Kingdom. So we list it with that backslash so you know it is the same book, and don't accidently buy the same book twice!
Alternate titles are very common for a variety of reasons. Some authors like to re-release books under a new title years later, for example.