I need to build an application on Mac OS X that runs on the background, windowless and provides a status icon in the top-right corner of the menu bar. It should launch on a specific action initiated by the user (not at system start up) and interact solely through the status bar icon.
On Windows this is very close to Services, on Unix - to daemons. What should i search for in Mac documentation? I just need a few keywords.
Nothing so strictly defined. Mac OS X considers the parts of your question to be separate concepts:
Having never programmed DOS or Windows, I have no idea what “resident” means to you. On Mac OS X, it simply means “in RAM”, which any running application at least partially is.
Services on Windows are not at all connected to this concept. A status item-only utility is the simile for something running solely from the system tray (like one of those delightfully useless nuggets that you get for seemingly every trackpad, audio card or GPU that you have the bad luck to be outfitted with). Services are just background programs a) without UI and b) that support or provide system or application functions. Dozens flare in and out of existence as you use Windows, mostly at startup, and most of them provide completely abstract functionality, such as providing network APIs for other services to use.
That said, Peter's answer is likely what you meant to find out, but I think it should be spelled out that it's not necessarily connected to the equivalent of Windows Services. (If you're looking to build such a thing on OS X, look up daemons and launchd.)