Feu is a type of agreement between a person and the owner of a piece of land. Imagine you're playing with your favorite toy car on a friend's carpet. Your friend owns the carpet, but they let you play with your toy car on it as long as you promise to take care of it and give it back when you're done. This is kind of like feu.
Feu is when a person is allowed to build a house or use the land for a certain amount of time, usually a really long time, like 100 years or more. The person who gets the feu has to promise to take care of the land and the house they build on it. They can also sell the feu to someone else, just like how you can sell your toy car to a friend. When the time is up, the feu ends and the land goes back to the owner or the owner's family.
One important thing about feu is that the person who gets it doesn't own the land, they just get to use it for a really long time. It's kind of like renting, but for a much, much longer time. Even though they don't own it, they can still take care of it and make it a nice place to live.