from The Century Dictionary.
- noun A stack or cock, as of grain.
- noun A rick of corn in the straw laid up in a barn.
- noun 3. In coal-mining, a space from which coal has been worked away, and which is more or less filled up with refuse.
from the GNU version of the Collaborative International Dictionary of English.
- noun (Mining) That part of a mine from which the mineral has been partially or wholly removed; the waste left in old workings; -- called also
- noun to remove the pillars of mineral matter previously left to support the roof, and replace them with props.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun mining That part of a
minefrom which the mineralhas been partially or wholly removed; the wasteleft in old workings.
from Wiktionary, Creative Commons Attribution/Share-Alike License
But experts said that the preferred theory was that a collapse of the mine's roof in the "goaf" - the void left behind after coal is removed - released methane into the mine.