Okay, so imagine that you and your friends are spinning around in circles. When you do that, you all have a center point that you are spinning around. That center point is called the barycenter.
Now, scientists use this concept of the barycenter to keep track of time in space. They use the term "Julian date" to refer to a specific date and time. But sometimes they need to take into account the fact that the Earth and other planets are all moving around the Sun, which means that their positions relative to the barycenter are constantly changing.
So, to make sure they are recording the correct time and date, they use a specialized measurement called the "barycentric Julian date." This takes into account the changing positions of the planets and adjusts the time accordingly.
It's kind of like if you were playing a game of tag, and you were trying to tag your friend who was constantly moving around. You would need to constantly adjust your strategy and movements to make sure you could catch them. That's kind of how scientists use the barycentric Julian date- they are "tagging" time in space and need to adjust their measurements to keep up with the movement of the planets.
Overall, the barycentric Julian date is just a fancy term that helps scientists keep track of time in space when things are constantly moving around.