What is the process of retreat mining where pillars are removed to let the roof fall in?

Pillaring refers to the method used in retreat mining where miners systematically remove support pillars that have previously been left in place to support the roof of the mine. This process allows the roof to collapse behind the miners as they advance, thus maximizing the extraction of the coal or other minerals. It is a strategic operation aimed at recovering as much of the resource as possible while ensuring safety by controlling the roof collapse.

Retreat mining itself encompasses various techniques, including the removal of these pillars, but "pillaring" specifically points to the action taken to facilitate the collapse. In contrast, room mining typically involves creating rooms by excavating coal while leaving pillars intact for support initially. Face mining doesn't precisely encompass the described process of pillar removal or roof collapse, as it's more related to advancing the mining face rather than the retreat phase.