book is one decorated by hand. The illuminations are of decorative
value, but are not considered to be part of the intellectual content
of the work. Thus when an illuminated book is copied it is the text of the work and not the illuminations which must be copied faithfully.
Not all illuminated works were hand written. The Gutenberg bible was printed, but much effort was spent in emulating a hand written work, including leaving space for illumination. Many of the copies of the Gutenberg bible held in the Library of Congress and the British Library were illuminated after printing.