The Book of Shadows (BOS, for short) are the notes Pagans/ Witches/ Wiccans have made along their journey of life and learning.
A Grimoire is a book of magic, spells and techniques.
People don’t always know there is a difference. It’s a pretty slight difference. The Book of Shadows would be less scientific and contain personal thoughts. However, both would have the facts and information about techniques for magic and spells.