Hi Weda,
as Henrique wrote, BuFw is the "backup firmware".
The C-Series and similar switches (SecureStacks, D-Series, G-Series, I-Series) can save two firmware versions on flash. The booted (running) version is shown as "Fw", the other as "BuFw".
The "Fw"/"BuFw" designation is adjusted automatically in contrast to EXOS' use of a "primary" and "secondary" partition.
Erik