Yazidis are a group of people who live in Iraq and believe in a religion that is different from most other religions in the world. Unfortunately, some bad people who follow the Islamic State (a group that wants to take over the world and make everyone follow their rules) did some very bad things to the Yazidis. They hurt them, took their homes and belongings, and even killed many of them.
These bad people did this because they didn't like the Yazidis' religion and wanted to make them follow their own religion. This is called "genocide" because it means that one group of people is trying to destroy another group of people just because they are different.
Luckily, many good people in the world are working hard to protect the Yazidis and bring justice to those who did them harm. They are trying to make sure that everyone is treated equally and with respect, no matter what their religion is.