What is Internal Revenue Certificate, as required by Norway as supporting papers for visa application?

Question

What does the form contains?

Answer 1

Are you a Norwegian citizen applying for a US visa, a US citizen applying for a visa to Norway, or a third country national applying for a visa to Norway? Please be specific.

If you are a Norwegian applying for a US visa, look here:
http://www.usa.no/embassy/consular/immigration/imminst.pdf
http://www.usa.no/embassy/consular/visa/checklist.html

If you are from somewhere else wanting a visa for Norway, all the information is here:
http://www.traveldocs.com/no/vr.h

None of these lists include an "Internal Revenue Certificate."