Ecological death is when a whole ecosystem (which is a fancy word for a big community of living things in a certain area, like a forest or a coral reef) is so messed up that all the plants and animals in it start to die off.
You can think of an ecosystem like a big puzzle where all the pieces fit together perfectly. There are lots of different plants and animals that depend on each other in the ecosystem, just like how you might depend on your family or friends. For example, bees rely on flowers for food, and flowers need bees to pollinate them so they can make more baby flowers.
Now, imagine if something really bad happens to the ecosystem, like someone knocks over the puzzle and all the pieces get mixed up. Maybe there's a huge forest fire that burns everything down, or people start polluting the water and killing all the fish. When something like this happens, the puzzle pieces don't fit together anymore, and the plants and animals that rely on each other can't survive.
As more and more plants and animals die, the ecosystem gets weaker and weaker until eventually, everything is gone. This is called ecological death, and it's really sad because it means that all the amazing and beautiful things that lived in that ecosystem are gone forever. So it's important for us to take care of our planet and not do things that might cause ecological death.