Boot Camp is a Mac OS X utility that lets you run Windows on your Mac without relying on virtual machines or crippled emulators. Boot Camp supports Windows XP, Windows Vista and Windows 7 (with OS X 10.6 or later). Boot Camp creates a Windows partition on your hard drive, along with the Mac OS partition. This means that none of your Mac content is touched at all, and Boot Camp has no effect on the operation of Mac OS.
The process of running Boot Camp to install a Windows partition includes running a preparation utility on Mac OS (after backing everything up of course), creating the partition and installing Windows, and then selecting which OS to boot into every time the machine boots up. To select an OS during startup you simply hold down the Option key and select the startup disk you want. Boot Camp gives you full access to all the power your MacBook or iMac have to offer, including all RAM, multiple processors and cores, 3D graphics, and all the ports.
Using your powerful Mac for both Mac OS and Windows used to require virtual devices, and while VMs have some advantages (allowing you to run both operating systems at the same time), for many users just being able to boot into either is all they want. Since Boot Camp is free, easy to install and use, and is supported by Apple, this is a winner of an app.