Hey kiddo, have you ever seen a car or a truck that runs on gas or diesel? Well, those are called fossil fuel vehicles because they use fossil fuels to power them.
Now, scientists have found that burning fossil fuels like gas and diesel can cause pollution and make the air dirty. This is not good for the planet or for the people who live on it.
So, many governments around the world have decided that they want to phase-out or get rid of fossil fuel vehicles. This means that they want to encourage people to use cars and trucks that don't use gas or diesel, but instead run on electricity or other cleaner fuels.
Some places already have laws that say that by a certain year, only electric or other clean vehicles will be allowed to be sold. This means that car manufacturers will have to make more clean vehicles so that people can still drive cars and trucks, but in a way that's better for the environment.
So, in short, the phase-out of fossil fuel vehicles means that people will start using cars and trucks that don't use gas or diesel but instead use cleaner fuels, so we can help protect the environment and breathe cleaner air.