What is the basic difference between Digital, Virtual & Hybrid libraries ?

In a short description for these three types of libraries, it could be mentioned that number of virtual libraries can form a digital library that can provide a sharing platform of resources. While, hybrid library mostly provide both the online and off-line services. For example, a hybrid library user can borrow a physical book at the same time he/she might access remotely a digital book using the library webpage to use the digital library.