Logical Names are a VMS (now OpenVMS) feature that allows the definition of virtual device names that map to filesystem paths. On Linux, logical names map a path prefix (some leading subset of a path) to another path.
Eventually, LLN will be a kernel patch with a modification to the VFS layer and a /proc interface for manipulating logical table entries. At the moment, however, only the lookup functionality has been written, I am still working on the kernel integration.
You can download the current source code here.