Tagxfs is a semantic file system. It extends the user space file system to a tag based hierarchy.
Imagine that you want to add a new folder to your existing folder structure. But semantically it belongs into more locations, e.g. you have the trailer for the movie 'Indiana Jones 4' and existing a folder structure (ref.1.1). It belongs in the folder Adventure and also in 2000s (production year 2008).