What's called _RMS_ in English is called _efficace_ in French
(meaning _effective_). There must be a related Dutch word. I'd
take this to mean that the input is calibrated for 0 dB = 4.38
Vpp.

In Italy we call it "efficace" too, and means RMS. It's not a kind of
semi-pro terminology at all.. maybe it suonds a little bit "old
style".. but it's still widely used in every university.
Ciao,
Pietro