Batch renaming is like giving a bunch of files new names, all at the same time. It's like when you want to clean your room, and you have a bunch of toys and clothes all over the floor. Instead of picking up each thing one by one and putting them away, you can gather them all up and decide on new places to put them all at once.
Here's an example: let's say you took a bunch of pictures of your family vacation, but when you uploaded them to your computer, they all had really long and confusing names, like "IMG_459823.jpg" or "DCIM9823749.jpg". You don't want to have to manually change each name to something more helpful, like "FamilyVacation_Beach.jpg" or "FamilyVacation_Mountaintop.jpg".
With batch renaming, you can select all of the pictures at once and give them all new names. You can even make each name slightly different, so that they each have something unique about them. For example, you could rename them "FamVacation_Beach_1.jpg", "FamVacation_Mountaintop_2.jpg", and so on.
This can save you a lot of time and effort, especially if you have a lot of files to sort through. It's like magic, where you can change the names of many things all at once, instead of doing it one by one.