If you connect your Mac to your TV, you might need to deal with TV Overscan. Explaining what it is and why TVs do it is complicated, but recognizing it is easy. If your TV screen cuts off the outer edges of your Mac’s image then you’re suffering from TV overscan. For example, you might not be able to see all of the menus at the top of your Mac’s screen or the lower half of the Dock icons might be cut off. If this is the case then you should figure out how to turn off the overscan feature on your TV.
If you want to understand what TV overscan is and why TVs do it, I’ll direct you to this article from Wikipedia.
My focus is try give you some guidance on how to turn off this feature. I recommend using your TV’s manual since television manufacturers use different terms, and the exact process varies from model to model. For example, I have a Samsung LCD TV. I eventually found a Picture Option named Just Scan.It turns out that this turned off overscan. The only clue that I was a parenthetical phrase in the manual which read, “Use the function to see the full image without any cutoff when HDMI, Component or DTV signals are input.” The feature’s name clearly didn’t give me a clue about what it does. I’ve learned that Samsung also sometimes calls the feature Screen Fit. Pioneer apparently calls this feature Dot by Dot. If you don’t have your TV manual hand you might be able to download one online. I typically find manuals by doing a Google search terms like this, “download Samsung LN42A550 manual.” Often the results will take me to a download link from the manufacturer’s site or a third party site which compiles user manuals.