DevFs is the Device FileSystem. It's optional starting with kernel 2.4.
It is designed so that instead of having to have a central body allocate major and minor numbers (unique identifiers) to devices, you can access them more like a namespace. For example, your serial port /dev/ttyS2 will become /dev/tts/2; console /dev/tty3 will become /dev/vc/3. You can still have support for the old names for software that would otherwise be confused by these changes.
You can find a detailed description of devfs at 
http://www.atnf.csiro.au/rgooch/linux/docs/devfs.html
3 pages link to DevFs:
