1) soil or amended soil used to fill the hole when planting a tree. 2) soil. conunon fill. aggregates or contaminants in various combinations put back after an excavation. May not be suitable for tree root growth and function.
Merriam-Webster Online Dictionary
backfill (verb)transitive verb
intransitive verb
to refill (as an excavation) usually with excavated material to backfill an excavation
backfill (Wikipedia)
This page is a glossary of archaeology, the study of the human past from material remains.