Short food supply chains are like when you get food from someone who lives close to you or from a store nearby. It's like when you go to the farmer's market with your parents and buy vegetables that were grown by a farmer who lives nearby.
When you buy food like this, there are fewer steps between the person who grows or makes the food and you who eat it. The farmer or store owner makes the food themselves or gets it from someone they know and don't have to travel far to bring it to you.
This is good because it helps the farmer and the storekeeper make more money, and it means that the food is fresher because it hasn't been sitting on a truck for a long time. It also helps the environment because there are fewer trucks driving around to bring the food to you.
So, when you buy food from someone who lives close to you, it's better for lots of reasons!