De-anonymization is the process of finding out who someone is when they don't want you to know. You know how you sometimes play hide-and-seek and cover your eyes and count while your friends go hide? De-anonymization is sort of like the opposite of hiding - it's when someone looks for you and tries to find you, even if you don't want them to.
When you use the computer or the internet, you can sometimes hide your name or identity so that people can't figure out who you are. This is called being anonymous. It's kind of like wearing a mask when you're playing dress-up - no one can tell who you are because they can't see your face.
But sometimes, people want to find out who you really are, even though you're anonymous. They might do this by looking at clues you leave behind, or by using special computer skills to track you down. It's sort of like being a detective - they're trying to solve a mystery!
There are different ways to de-anonymize someone. Sometimes, people might look at what you're doing online, like what websites you're visiting or what you're typing into the computer. They might also look at things like your IP address, which is a special code that tells the computer where you're located.
Other times, people might use social engineering to find out who you are. This means they might try to trick you into revealing your identity, like by pretending to be someone else or by using fake information to get you to tell them stuff.
In general, de-anonymization is a way for someone to find out your true identity, even if you're trying to keep it a secret. So you always have to be careful when you're on the internet and make sure you're doing things that are safe and won't give away too much information about who you are!