What is 'Run as Administrator' in Windows 7? [duplicate]

On my Windows 7 machine, I am an administrator. I see, when I right click an app, it has an option Run as Administrator. What does this mean?

Also, if I am logged in as administrator, what significance does this have: Run as Administrator? Why does it need to be mentioned explicitly?

On Windows 7 (as well as Vista), an administrator account does not necessarily run a program with administrator priveleges. As an administrator, you have the credentials to perform administrator functions (creating/modifying user permissions being one of them, etc.). However programs are still run in a secured mode, in which they are prevented from doing specific functions (access to certain hardware/software properties, etc.). To allow access to these properties, you can run a program in "run as administrator" mode which grants access. For specifics on what can and cannot be performed, I would search online or read up on the Microsoft developer websites.

Under XP, the privileges given to applications you launched were the same as those you would get interacting directly with the OS. Under Vista and 7, they're not - unless you deliberately choose to use your powers by elevating the application; choosing Run as Administrator is one way to elevate an application. (Some apps are marked as only making sense when run as admin so when you run them you'll get the dialog even though you didn't choose Run as Administrator.)

Vista also moved the boundaries of what you need admin powers for. Under XP you needed to be an admin to change the time zone, or to switch the calculator from standard to scientific. As a result pretty much everyone was an admin. Plus developers (who were all admins because they installed things often) all tested as admins and their stuff worked, so they shipped it, and then found out it only worked for admins - a bug they generally solved by making all the users admins. The problem with that was malicious code (you may have heard a lot of malicious code targets Windows) could likely run with high powers and mess up your machine.

Under 7, you can live a pretty ordinary life without elevating unless you're installing something, and you always know whether you're using your admin powers or not. Non elevated apps can't write anywhere under Program Files, can't write to some parts of the registry, and so on. But if the app is well written, that won't be an issue for you. Sometimes when you have an old app (say from XP times) that doesn't seem to work properly on Vista or 7, people will suggest you run it as administrator. But in general, pay it no attention and you'll be fine.