Composing and arranging music are loosely related, in that somebody sits down and writes out the music, but they are completely different concepts. Basically, composition is an act of bringing something into existence. Arranging is reinterpretation, expansion, or the movement of a piece of music into a different context.
Music that has been copied from the original into a different instrumentation are considered transcriptions.
This category is for general information about arranging.
Make sure of the legality of your arrangements before marketing them.