Thirty pieces of silver

OK kid, back in the olden days when people used money made of actual metal, thirty pieces of silver was a specific amount of money that was mentioned in a story. This story is in a really important book called the Bible, and it's about a guy named Judas who was a friend of Jesus.

Judas decided to betray Jesus and turn him over to the Roman leaders who wanted to arrest him. Judas went to them and said he would help them find Jesus, and they agreed to give him thirty pieces of silver in return.

So, thirty pieces of silver became infamous because they represented a terrible act of betrayal. It's like if you had a friend and you promised to keep their secret, but then you went and told everyone anyway for some money. That would be a bad thing, and that's what Judas did to Jesus.

In general, people use the phrase "thirty pieces of silver" to talk about the idea of betrayal or selling out someone for money. It's a reminder that money isn't everything and that some things, like friendship and loyalty, are much more valuable.