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.
Although the original plan was for the hole to be drilled to 15,000 meters (49,000 ft), the project was unable to proceed due to the temperatures encountered. In recent years a few longer boreholes have been drilled, but the Kola Superdeep Borehole still holds the record for the deepest artificial point on earth.