Definition of "backfill"

backfill

verb
third-person singular simple present backfills, present participle backfilling, simple past and past participle backfilled
1. To refill a hole with the material dug out of it.
  Quotations
  Clay excavated for the new river channel has been used to backfill the old watercourse, while embankment vegetation was also moved from the old channel to the new in order to preserve a habitat for the rare Four Spotted Moths that live there.
  2020 April 8, Paul Stephen, “ECML dive-under drives divergence”, in Rail, page 43
2. (archaeology) To refill an excavation unit to restore the former ground surface and/or to preserve the unit and make it recognizable as having been excavated.
3. (US) To provide reserve support.
4. (US) To replenish or restock due to attrition or loss.
5. (gaming) To enter an online game that's already in progress, replacing a player who left early.
noun
countable and uncountable, plural backfills
1. The material that has been used to refill an excavation.
2. (US) Reserve support personnel.
3. (US) That which backfills; a replacement.
4. (literature) Material in a story set earlier in the past, providing history or context for the current action.