A group boycott is when a bunch of people decide to stop working with or buying things from someone else, usually because they don't like something that person did or said.
Imagine you and your friends all really loved playing a certain game together. But one day, one of your friends did something mean like cheating or not playing fairly. All of your other friends agreed that they didn't want to play with that person anymore. So, you and your friends decided to stop playing with the cheater and only play with each other.
That's kind of what a group boycott is. It's when people team up and refuse to associate with someone because they don't like what they did. This can happen in real life, like if a bunch of people decide to stop buying things from a certain store or not watching a certain TV show. Or it can happen online, like if a group of people decide to stop following someone on social media.
It can be really powerful because if enough people boycott something or someone, it can really hurt their business or reputation. But it can also be risky because sometimes people can be peer pressured into boycotting someone they don't really understand or fully agree with, without really considering the consequences.