A lay judge is a person who helps decide if someone is guilty or innocent in a court case. They are not a professional judge and do not work in a court all the time. Instead, they are regular people who are chosen to be a judge for just that one case.
Lay judges listen to what the lawyers and any witnesses say, and they also look at any evidence that is presented in the case. They then decide if they think the person on trial is guilty or not guilty.
Lay judges can be picked in different ways depending on the country. In some places, they are picked randomly from members of the community. In other places, they are chosen by a government official.
Some people think having lay judges is good because they bring different perspectives to the legal system. Others think it's bad because lay judges may not have the legal knowledge of a professional judge.