The European Union is a group of 28 countries in Europe whose governments work together. It is often referred to simply as the EU.
Countries that are members of the EU agree to follow a set of shared rules and they receive certain benefits in return.
One of the main aims of the EU is to make it easier for countries in Europe to do business with each other. It can also help with things like making it easier to catch criminals.
The UK is a member of the EU.