An illuminated manuscript is a book or manuscript decorated by hand with richly colored ornamental letters, designs, or illustrations. Especially prevalent during the Middle Ages when books were handwritten on parchment or vellum. Prime examples are the Book of Kells and the Lindisfarne Gospels.
Illumination is the decoration of an initial letter or word in a manuscript with designs or tracings in gold, silver, or bright colors, or to decorate a manuscript page or border with initial letters, miniature pictures, designs, etc. It is most often seen in medieval manuscripts.