Fortress conservation means protecting nature by isolating it from humans. Imagine you have a favorite toy that you don't want anyone else to play with, so you put it in a box and keep it away from your friends. In the same way, some people think that protecting land and animals is best done by putting a big fence around it, and not allowing people to go inside. They build this "fortress" around the land, with guards and cameras, to keep humans out and let nature thrive.
This type of conservation started because people thought that humans were causing too much damage to the environment, like cutting down trees, killing animals or polluting the air and water. They said that if we kept people away, nature would heal itself and be saved. But some people think that we need to work WITH nature, not against it, and that conservation should be a more collaborative effort.
So, while fortress conservation can be really helpful in protecting land and animals in some cases, some people believe there are other ways to achieve the same goals without isolation.