In the OpenSolaris world, this is a way to upgrade a subset of your system's binaries using cpio archives instead of packages. But the BFU tool itself was developed very long ago in the early days of the Solaris Kernel around 1993. The original idea came from Roger Faulkner and Jeff Bonwick wrote a Shell Script to implement Faulkner's idea. That shell script has matured and witnessed revisions to become the BFU tool that is widely used in the OpenSolaris world today.

Originally BFU was internally known amongst developers as Big F'ing Upgrade. But it was later refined to be "Blindingly Fast Upgrade" or "Bonwick/Faulkner Upgrade".

This is not a recommended method for end users to upgrade their systems but the OpenSolaris developers and community enthusiasts wanting the latest features on their machines use this as an extremely fast way to upgrade the bits on their machine instead of spending hours and hours compiling code.