A man-in-the-middle attack is when someone tries to sneak in the middle of a conversation between two people or computers to get information. They are trying to get access to private information that they shouldn't have and they are like a sneaky spy! For example, a person in the middle might try to get access to your bank account numbers when you are trying to log in to a bank website. They will try to trick you by posing as a legitimate website and stealing your personal information like your bank password. This can be really dangerous so it's important to always make sure the website you are using is authentic and secure.