What does it mean when the catalog says a book is "In Transit"?

Question:
I am looking for the book:

Probabilistic graphical models :
principles and techniques by Daphne Koller

The online library catalog
says that this book is "in transit". What does this mean?

Answer: 

"In transit" means that the book has been sent from one library to another library, and hasn't arrived at the sent location. This probably means that it has been returned to a different branch library, and is being returned to its home library (in this case, the Mathematics and Statistics Library), but it could mean that it is on its way to another location for repair, or relocation. You should contact the Math & Statistics Library for details on this book's status.