"Pillar mining" is not a commonly recognized term in the mining industry. It's possible you may have heard a similar term or a phrase that sounds like it.

Here are some mining terms that might be related, and what they mean:

* Pillar Extraction: This is a method used in underground mining where the miners remove material, leaving behind pillars of rock or coal to support the roof. These pillars are designed to be strong enough to prevent cave-ins. After some time, the pillars themselves may be extracted in a controlled manner.

* Longwall Mining: This is a highly mechanized method of underground coal mining where a large machine cuts a long, continuous wall of coal. The roof behind the machine is allowed to cave in, and the material is transported out of the mine on a conveyor belt.

* Room and Pillar Mining: This is a traditional method of underground mining where miners create a series of rooms and leave pillars of material between them to support the roof.

* Underground Mining: This is a general term for any mining operation that takes place below the surface of the earth.

It's important to be specific with mining terms to avoid confusion. If you can provide more context or the exact phrase you heard, I can give you a more precise answer.