WATCH: What is radiation?
The earthquake in Japan has damaged a nuclear power plant which is now leaking radiation.
People living in the area have evacuated their houses while workers try to get everything under control.
What is radiation?
Radiation is a way that energy or heat moves around. Low levels of radiation are everywhere - this is known as background radiation. The sun, soil, rocks and animals all give off low levels of radiation.
A nuclear power plant produces a high level of radiation but this is contained within the reactor.
Is radiation dangerous?
Radiation damages the cells that make up the human body.
Low levels of radiation are not dangerous. Medium levels can lead to sickness, headaches, vomiting, and a fever.
High levels can kill you - by causing damage to your internal organs. It's difficult to treat high radiation exposure.
Plus, in the long-term, exposure to radiation can cause cancer.
How dangerous is the Japanese nuclear power plant?
It's thought that only emergency workers at the plant are at risk of harmful doses of radiation, but it's likely they are only being exposed for short lengths of time so there's less danger.
The level of exposure for people living close to the plant was a lot lower, and there should be little risk to people living further away.