word choice - Which is more correct: "Plug-in" or "plugin"?

What is the correct word, plugin or plug-in? Does it depend from the context?

Answer

As others have mentioned, most dictionaries (including the OED) list plug-in as appropriate. I'd seriously shy away from calling plugin incorrect—I mean, just look how many hits you can get with Firefox and plugin. In my experience, especially with computer programs and on the Internet, plugin is much more common than plug-in. Taking a descriptivist standpoint, I'd put my weight behind plugin.