Definition of backfills:
(v) :
To refill a hole with the material dug out of it.
(v) :
(US) To provide reserve support.
(v) :
(US) To replenish or restock due to attrition or loss.
(v) :
(gaming) To enter an online game that's already in progress, replacing a player who left early.
(n) :
The material that has been used to refill an excavation.
(v) :
(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.