Qubes is a security-oriented operating system (OS).
Qubes takes an appraoch called security by compartmentalization, which allows you to compartmentalize the various parts of your digital life into securely isolated virtual machines (VMs). A VM is basically a simulated computer with its own OS which runs as software on your physical computer. You can think of a VM as a computer within a computer.
This approach allows you to keep the different things you do on your computer securely separated from each other in isolated VMs so that one VM getting compromised won’t affect the others. For example, you might have one VM for visiting untrusted websites and a different VM for doing online banking. This way, if your untrusted browsing VM gets compromised by a malware-laden website, your online banking activities won’t be at risk. Similarly, if you’re concerned about malicious email attachments, Qubes can make it so that every attachment gets opened in its own single-use, “disposable” VM. In this way, Qubes allows you to do everything on the same physical computer without having to worry about a single successful cyberattack taking down your entire digital life in one fell swoop.
“I’m really exited about Qubes” Eduard Snowden