Making the world better, one answer at a time. They are referring to the volume, in this case of an approximate rectangle. So say your refrigerator was 6 feet tall (inside not outside), and 3.5 ft across and 3.5 ft deep.
The Kola Superdeep Borehole on the Kola peninsula of Russia reached 12.262 kilometres (7.619 mi) and is the deepest penetration of the Earth's solid surface. The German Continental Deep Drilling Program at 9.1 kilometres (5.7 mi) has shown the earth crust to be mostly porous. Drillings as deep as 2.1 kilometres (1.3 mi) into the seafloor were achieved at DSDP / ODP / IODP Hole 504B. Because the continental crust is about 45 km thick on average, whereas oceanic crust is 6-7 km thick, deep drillings have penetrated only the upper 25-30% of both crusts.
It is now over 40,000 feet deep, making it the deepest hole on earth (the previous record holder was the Bertha Rogers well in Oklahoma--a gas well stopped at 32,000 feet when it struck molten sulfur). It is not oil or gas that is being sought with the Kola well, but an understanding of the nature of the earth's crust.