Hello Ingmar.

The Dutch word "doorloop" is not in common use anymore, but it referred
to a covered (as in protected from the elements) passage way, where in
the hore and buggy days passengers could be loaded up during inclement
weather. One could frequently find such a "doorloop" in country inns
(called"herbergs") although not limited to those alone. I don't know
what it means when used in organ jargon, but the most likely meaning
there could be a passage way of one area to another. I could also, in
a broad sense, refer to a shortcut from one area to the next. In my
days as a younbster in Holland the name was still used by "oldtimers"
for any covered passageway that lead from one area to another.

Any help? What do the other dutchman have to say about its meaning ?
I am curious because the dutch language is full with words that have
different meanings depending on the structure they are used in.

Albert de Boer