A master of the horse is a person who takes care of horses for really important people, like kings or queens. They make sure the horses are healthy and happy, give them food and water, and make sure their stables are clean.
Sometimes, the master of the horse would also help choose which horses the important person would ride for special events, like parades or battles. They would make sure the horse was trained well and ready to go.
The master of the horse was a very important job back in the olden days when horses were a big part of transportation and fighting. They helped keep things running smoothly for the important people they worked for.