• (n.) That part of a mine from which the mineral has been partially or wholly removed; the waste left in old workings; -- called also gob .
Goaf ; noun ; plural Goafs or Goaves . [ Confer lst Gob .] (Mining) That part of a mine from which the mineral has been partially or wholly removed; the waste left in old workings; -- called also gob . To work the goaf or gob , 
gob (def. 3).