The Canonical hours are divisions of time, developed by the Christian Church, serving as increments between the prescribed prayers of the daily round. A "Book of Hours" contains such a set of prayers.

Office of Readings or Morning Prayer (Matins), major hour
Morning prayer (Lauds), major hour
Daytime prayer, which can be one or all of
Midmorning prayer (Tierce)
Midday prayer (Sext)
Midafternoon prayer (Nones)
Evening prayer (Vespers), major hour
Night Prayer (Compline)

A Book of Hours is the most common type of surviving medieval illuminated manuscript. Each book of hours is unique in one way or another, but all contain a collection of texts, prayers and psalms, along with appropriate illustrations, to form a reference for Christian worship and devotion.

For more information and a few images: Book of Hours