SpeechRecognition is the technology that allows a user to speak commands and have the program interpret them and perform actions. It’s not all things to all people (that is, it isn’t always useful), but it is a form of UserInterface that is available to you when developing your Mac OS X applications.
Anyone interested in porting sphinx (http://fife.speech.cs.cmu.edu/sphinx/)? It would make a great addition, methinks.
-jason