What is a tag-based file system

Tag-based file system is a concept for a file system that instead of using folders uses tags. Usually tag based system is thought of when thinking about how normal files and folders file structure is flawed in a major way: if you have a file that fits under 2 (or more) categories where do you put it? Example: lets say you have a meme thats also cat and folders "cats" and "memes" do you:
A) duplicate the image
B) duplicate the folder and put in the diffirent one and put image in the deeper folder
C) use symlinks
As you can see normal File Systems get messy and they are hard to use