Iata o definitie aici:

Musical register may be:

1. The general pitch that an instrument is known for; the overall stretch of an instrument’s voice. For example, the cello has a lower register than the violin*. In sheet music, register is signified by a clef.

2. In organ music, a register is a set of pipes (or “rank” of pipes) of one length, responsible for a specific octave or timbre. In stringed keyboard instruments, a register is a choir of strings.

3. Organ stops may be referred to as registers; the act of alternating stops is called “registration.”
http://piano.about.com/od/musicaltermsa1/g/GL_musical-regist...

Si un exemplu, aici: "the employment of wide registration"...
http://books.google.ro/books?id=Pgj6VuAf2tcC&pg=PA264&lpg=PA...