What is the meaning of back fill?

Answer 1

Back fill is an excavation term that means putting the dirt back in the hole or the dirt that was put back in the hole.

"Billy-Bob laid the water line but his backfill was full of sharp rocks. That's why he's digging it up again."

By analogy, the term is figuratively applied to similar circumstances such as re-constituting staff by transferring from other departments.