Let's say you and your friends are playing a game together. If you have an umpire or a judge that decides who wins and loses the game, it means the game is juried. But if no one decides who wins or loses, the game is unjuried. It's like playing tag with your friends – there's no judge to decide who is "it" or who wins, you just play and have fun.
In other words, "unjuried" means there is no person in charge of judging or deciding who wins or loses in a particular situation. It's like leaving things up to chance and letting people decide for themselves. This can be fun in games or contests, but for more serious situations, like a court case or a competition with high stakes, having a judge or umpire is usually necessary.