Low Orbit Ion Cannon

Low orbit ion cannon is a computer program that can make lots of fake signals to flood a server or website with requests. It's kind of like having a lot of people try to knock on a door at the same time to overwhelm the owner and prevent them from answering the door to legitimate visitors. People use it to try and shut down websites or servers as a way of protesting or causing harm. It's not a nice thing to do and can be illegal. Just like it's not nice to flood someone's mailbox with junk mail.