Hmm, that is an odd word, sounds like someone made it up! Oh! They did! This term was first coined by Christopher Small in 1987 and he subsequently wrote a book about it, entitled Musicking: The Meanings of Performing and Listening. Musicking is a verb, an 'action word' which he argued should be placed in the dictionary, to describe our act of being involved in music. I think it is a rather funny sounding word, to suddenly use it as a verb feels a bit odd... but I'm not beyond embracing a new (old) idea!