Have you ever used a coloring book and accidentally colored outside of the lines? Overprinting is kinda like that, but with printing paper.
When we print something, we use different colors to make an image or text. Sometimes, we want those colors to overlap (or overprint) on top of each other to create a new color or effect.
But just like coloring outside the lines, if we're not careful, overprinting can make the colors look messy or not how we want them to. So, printers have to be really careful when they set up their machines to make sure the different colors overlap in just the right way.
Overall, overprinting is just a fancy way of saying we're mixing colors together to make something new and cool-looking.