The process of mining a seam of minerals (e.g. coal, marble) that exists just under the surface of the earth in the most efficient and cost effective way possible.
Basically, you just get a big digger and rip the topsoil and vegitation away until you get at whatever it is that you want.
Traditionally, once you have exhausted the seam, you then bugger off and leave a huge, ugly, sterile hole in the ground.
You get extra bonus points if you manage to poison the groundwater with some nasty by-product such as a heavy metal, cyanide, or suchlike.

A really nasty way of treating the planet, much akin to date rape.