Imagine you have a toy puppet that looks like you, and you use it to pretend like you are someone else. That's kind of like what sockpuppetry is.
On the internet, people sometimes pretend to be someone else by creating a fake account. This fake account is called a sockpuppet. They can use this fake account to say things they wouldn't normally say or to pretend like a lot of people agree with them.
For example, if someone wants to make it seem like a lot of people like their post or comment, or if someone wants to make it seem like a lot of people hate someone else, they might create a bunch of sockpuppet accounts to make it seem like a lot of people feel that way.
Sockpuppetry can be bad because it's not honest, and it can make it hard to know what real people really think. It's important to always be honest and true to yourself when you're online, even if other people don't agree with you.