Special Master is a person who helps a judge to make decisions about a case.
Let's pretend that you and your friend have a big fight over who gets to play with a toy car. Your grown-ups might help you by bringing in a special master to talk with you and your friend.
The special master will listen to both your sides of the story, and then help you and your friend find a solution that's fair for both of you.
In big legal cases, sometimes there are a lot of people arguing about different things. The judge might need help from a special master to sort out all the arguments and information. It's like the special master is another grown-up who knows a lot about the case, and helps the judge make a fair decision.
So just like when you and your friend needed help with the toy car, sometimes grown-ups need help too, and that's where the special master comes in!