A user account type available in Windows XP Home Edition and Windows XP Professional. "Limited" users may run installed applications and work with their own files on the computer. They may also read files created by other users stored in Shared Documents. They may not install most applications, install device drivers, change another user's files, or otherwise alter the computer itself.
Equivalents in other operating systems include Restricted User in Windows 2000, and just plain "user" in Windows NT and most POSIX systems including Linux.
Since the limited user account cannot make system-wide changes, the system can prevent most computing problems before the fact. This includes stopping unknown viruses and other unwanted software from running on the computer, or at least limiting the damage they can do.
Applications and devices Designed for Windows XP work correctly when used with a limited user account. Products without this certification may also work, but as of mid-2005, the majority of new applications without this certification do not. Microsoft's Windows Catalog is a list of products with this certification. There may also be one or more Anti-Windows Catalogs of products to avoid.
Ironically, most unwanted software (viruses, spyware, etc) weren't tested in this environment, so using a limited user account for your daily work prevents virtually all unwanted software. When such software finally works with limited user accounts, you will only need to create a new account and delete the old one to remove it.