The Book of Hours was a devotional book popular
in the later Middle Ages.
It is the most common type of surviving
medieval illuminated manuscript.
Like every manuscript, each manuscript book of hours
is unique in one way or another, but most contain
a similar collection of texts, prayers and psalms,
often with appropriate decorations,
for Christian devotion. Illumination or decoration
is minimal in many examples, often restricted to
decorated capital letters at the start of psalms
and other prayers, but books made for wealthy
patrons may be extremely lavish, with full-page miniatures.
BNF - L'Aventures des écritures. Matières et formes :
Livre d’heures à l’usage d’Amiens