When you go to a music concert or a show, there are people who may secretly record the performance without permission. This is called bootleg recording. They do this by hiding a small recording device in their pocket or bag and then pressing a button to start recording.
It's like when you play "hide and seek" and your friend tries to hide behind a tree so you can't see them. Bootleggers do the same thing with their recording device and try to hide it so that nobody notices.
Sometimes, people who make bootleg recordings will sell them to other people who couldn't attend the concert or show. This is not allowed because the artist or performers didn't give permission for their performance to be recorded and sold. It's like taking a toy that doesn't belong to you and trying to sell it without asking first.
Bootleg recordings can be bad for the artist or performers because they can lose money if people buy the bootleg instead of the real thing. It's like if someone offered you a toy that doesn't work very well, but you still wanted to buy it instead of the brand new version that works perfectly.
Overall, bootleg recording is not a good thing to do because it's not fair to the artist or performers and can cause them to lose money. It's important to always ask for permission before recording someone else's work.