Aristocracy is a fancy word for a special group of important people in a society. Imagine you and your friends are playing a game of knights and princesses. In this game, one of your friends might be the princess and you could be the knight. Now imagine that in real life there is also a group of people who are like the princess - they are born into a special family that is very important in their country. This group of people is called the aristocracy.
In the old days, the aristocracy was made up of kings, queens, princes, and princesses who ruled over their countries. But nowadays, the aristocracy might be made up of rich families who have a long history of being important in their communities. They might own large estates, castles, and have fancy titles like "Duke" or "Earl."
The aristocracy used to have a lot of power and influence, but in most countries today, they don't have much say in how the country is run. They are still important because they are often very wealthy and can afford to live in luxury. People might look up to them and admire their lifestyle, but they don't have any official power.
So, in short, aristocracy is a group of special people who are born into important families and are often very wealthy, but don't have much power in modern societies.