I'm not in the AI field, but what does "synthetic data" really mean? I'm seeing different definitions in the comments. If I were to add synthetic lens flare to

I'm not in the AI field, but what does "synthetic data" really mean? I'm seeing different definitions in the comments. If I were to add synthetic lens flare to an existing image, would that be synthetic? Change the white balance? Add dirt, scratches, replace paint colors, etc? Change someones skin tone? Add blemishes? Knowing nothing, all of these seem like they would be very beneficial, but I always see people saying any synthetic data is bad data. With the probability of intercept being so incredibly low for some of this stuff, I can't see how that could be true.