Why does the entry 'sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0' exist in /etc/mtab ?

Issue

• Why is the entry 'sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0' seen in /etc/mtab ?

  # mount
  /dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)
  proc on /proc type proc (rw)
  sysfs on /sys type sysfs (rw)
  devpts on /dev/pts type devpts (rw,gid=5,mode=620)
  /dev/vda1 on /boot type ext3 (rw)
  tmpfs on /dev/shm type tmpfs (rw)
  none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
  sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)