Setaouti Samir, you can see virtualization as concept of connecting remote locations together and serving your clients on different Cloud models. For me, when I was under my Minor Project Development, I use VmWare tools to create a virtualized Cloud topology using CISCO Router and Switch.
Basically, Virtualization is the implementation of web applications onto data center at backend.
That's what I know about Virtualization and hope this would help you to understand much.