Diesel fuel is a type of fuel that is used to power big vehicles, like trucks and buses. It's different from the kind of fuel you might use for a car, which is called gasoline.
Diesel fuel is made from a few different things, but the main ingredient is crude oil. Crude oil is a type of oil that comes from underground and needs to be refined before it can be used to make diesel fuel.
Once the crude oil has been refined, it goes through a process called "cracking," which breaks it down into different parts. The parts that are used to make diesel fuel are called "distillates."
Diesel fuel is special because it burns very cleanly and efficiently, which means that it doesn't produce as much pollution as other types of fuels.
Although diesel fuel is mostly used for big vehicles, it can also be used to power generators and some types of boats.