Synthetic lethality is like two things that are not dangerous on their own, but when they are together, they become very bad and might even stop cells from working. It's like when your mom or dad tells you not to mix bleach with ammonia, because it can create a harmful gas.
In science, researchers study cells and how they work in the body. They look for ways to stop cells from growing or doing bad things, like causing cancer. Synthetic lethality is a way to stop cells from growing or working by targeting two different things at the same time.
For example, imagine there are two proteins in a cell. Normally, each one is not harmful on its own, but when they are both working at the same time, it can cause the cell to die. Scientists can design a drug that targets one of the proteins, and another drug that targets the other protein. When both drugs are given together to the cell, they become very bad together and can stop the cell from working, which can help treat cancer.
So, synthetic lethality is like a sneaky trick that scientists use to stop cells from growing or working by targeting two different things that are not harmful on their own, but become very bad when they are together.