What is User Account Control?

User Account Control (UAC) is a new security component in Windows
Vista. UAC enables users to perform common tasks as
non-administrators, called standard users in Windows Vista, and as
administrators without having to switch users, log off, or use Run As.
A standard user account is synonymous with a user account in Windows
XP. User accounts that are members of the local Administrators group
will run most applications as a standard user. By separating user and
administrator functions while enabling productivity, UAC is an
important enhancement for Windows Vista.