what's the counterpart of a Windows service on Mac OSX

On Windows, we call somethin开发者_开发知识库g running at background as service. What about on Max OSX, is there such thing? what is it called?

They’re called agents or daemons. See this other question.

I would say that the closest analog is a launchd service.
Launchd is Apple's replacement for init and cron, among others.

http://en.wikipedia.org/wiki/Launchd