Hi there! Do you know what a knight is? A knight is someone who is really good at fighting and usually has to protect a castle or kingdom. In the olden days, a knight would be given some land to help him pay for his armor, weapons, and horses. This land was called a knight's fee.
It's kind of like when you get an allowance from your parents for doing your chores. The knight's fee was like the allowance for the knight for protecting their kingdom. The knight would have to pay some of the money he made from the land to the king or lord who gave him the land. This was like the knight paying a special tax for the land he was given.
Sometimes, the size of the knight's fee was a lot of land, and sometimes, it was only a little bit. The bigger the land, the more important the knight was considered. Knights who had bigger fees were usually more powerful and had more influence.
So, in summary, a knight's fee was like a special allowance given to a knight to help him pay for things he needed to fight and protect the kingdom. This was in exchange for the knight protecting the kingdom and paying taxes to the king or lord who gave him the land.