Footwall and Hangingwall can be thought of as Above or Below. As Mucker stated its a mining term in reference to where you are relative to the orebody.

The Hangingwall is above the orebody and the Footwall is below the orebody. As Old Joe stated it is also used in structural geology for stating which rock is above or below a fault but its main and historical use relates to mining. There are many deposits that have been overturned due to folding of the earth's crust so the hangingwall can in those cases be younger than the footwall.

From a mining perspective you alomost always put your access points like ramps/inclines, shafts, drift, vents etc into the footwall of the deposit so that they are in stable rock and don't interfer with mining the orebody. If you put a shaft, decline, etc through the hangingwall of an orebody you need to leave the rock around it undesturbed. The space around it could easily be 30+ meters (in every direction) in stable rock and more in unstable conditions. So if you went though a 40 meter thick orebody with a shaft you would tie up say (30*30*40) ~36000 cubic meters of ore.

... Been There