An agricultural union is like a big group of people who work on farms coming together to help each other. It's like your friends at school who help you with homework, but instead of homework, they are helping each other to sell their crops and animals for a fair price.
You know how you have rules at school? Agricultural unions also have rules called "collective bargaining agreements." These rules help farmers to make sure they are paid enough money for their hard work, and that their working conditions are fair and safe.
Just like how your class might have a leader or teacher, agricultural unions also have leaders who help organize the group and make sure everyone is treated fairly.