A book of hours is a special kind of book that people used to have a long time ago to help them pray at specific times during the day.
It was called a book of hours because it was divided into different sections that corresponded to different times of the day, or "hours." Each section had its own special prayers, songs, and pictures that helped people focus on their spiritual thoughts.
The book was very beautiful and decorated with pictures of religious scenes and different colors. People would often carry it around with them and use it to pray when they had a few free moments throughout the day.
The book of hours was a very important part of many people's daily lives, especially in the Middle Ages, when most people were very religious. It helped people to feel closer to God and to remember important things they wanted to pray about throughout the day.
So, a book of hours was a special book that helped people pray at different times of the day, and it was very pretty and important to many people a long time ago.