It is a concept of using multiple operating systems on a same device without using additional hardware. The concept of virtualisation can be of great help if you are a developer, this concept is widely used in cloud architecture.

Pros:

• All the operating systems are completely isolated from each other, therefore hacking one sytem will not give access to other.
• Developers can test their codes on different platforms without using additional machine.
• There is no limit in creating operating systems in host machine till sufficient resources are there.
• Used in cloud technologies on server machines.
• Operating systems can be installed without any host operating system, which is also used in server machines.
• Data loss of one OS will not affect other Os.

Cons:

• The other operating systems share the resources of host opearting system like RAM,Hard disk etc.

Most commonly used virtualisation tool are VM box by Oracle and Hyper-V by Microsoft.