An instance dungeon is like a special play area in a video game that you can only go into with your friends or other players. It's like if you had a secret clubhouse that only you and your friends could go into and play games together.
When you go into an instance dungeon in a video game, you are in a special area that is just for you and your group. You won't see other players who aren't in your group in there. You might have to do special tasks or fight enemies to get through the dungeon, and at the end, you might get special rewards like treasure or cool items.
Instance dungeons are a way for players in a video game to work together as a team and have fun playing together. They also make it easier for the game designers to create challenging levels that players can conquer with their skills and teamwork.