These are third-party applications that run on your Mac just like any other program. You can either install Windows in Boot Camp, a native feature of the Mac OS X operating system, or you can use a virtualization program. If you are looking to install Windows on your Mac, you have two options.
This is especially useful for individuals who want to use Macs but may rely on a few programs that are Windows-specific. While you need to purchase a copy of the Windows operating system separately from your Mac, once you do you can install it and enjoy the benefits of both operating systems. These individuals overlook a key feature of the Mac lineup - you can run Windows on them. In the classic 'which is better' argument between Macs and PC's, PC advocates sometimes bring up features or characteristics of the Windows operating system as an argument for PC's being better than Macs.