Virtual machine. It is basically a program you can open that functions like a separate computer. The program dedicates some hardware resources and you install an OS of your choice. This has miltiple advantages: for the described purpose in the example above, the VM provides you with a fresh machinewhere you have not done any customization that would make you identifible. Other uses include e.g. using Windows software inside a Linux installation or experimenting with viruses (which would usually attack the sandboxed VM and not your actual OS).