the.com/wellbore

means The drilled hole, from surface down to the reservoir, that forms the physical passage of an oil, gas, or water well.

from A straightforward compound from drilling and mining language: 'well,' the old word for a dug or drilled source of water (or, later, oil), plus 'bore,' meaning a hole made by boring or drilling — the same 'bore' as in 'borehole' or a gun's bore. Put together, 'wellbore' names exactly what it is: the cylindrical hole bored to make a well. The term rose with the petroleum industry in the 1800s–1900s as engineers needed a precise word for the hole itself, distinct from the casing, the fluids inside it, or the well as a whole operation.