A fortified house is like a really strong castle where people used to live in the past. It has lots of features that make it very hard for bad guys to get in.
Imagine your favorite toy box that you want to protect from your little brother or sister. You would put it in a very strong box that only you know how to open. You would also put locks on it so that nobody else can open it.
In the same way, a fortified house has really thick walls made of stone, which make it super hard to break in. The windows in a fortified house are also very small, so bad guys cannot enter through them.
Now imagine that someone did manage to get past the walls and windows. They would still need to get past other obstacles, such as a drawbridge, a portcullis, and even more doors. These features are like traps in your favorite game that bad guys keep falling into because they cannot figure out how to get past them.
Lastly, a fortified house usually has a watchtower where someone can keep an eye on everything that is happening outside. This person can then warn the people inside if they see any danger approaching.
So, in summary, a fortified house is a really strong and protected place where people used to live a long time ago to keep themselves safe from bad guys.