I just wanted to comment further on Louise's answer, even though I can't unfortunately suggest a better one! But stage lighting IS my field...

So: what is being described in Louise's answer seems to be a 19-inch rack --- which is quite universal in the entertainment (and other) industries. The odd thing is, this terminology is used both sides of the Atlantic, whilst 'system stand' seems to me very dodgy indeed, and in view of the fact that it comes from the OLF, suggests maybe a poor translation from Ca. French in the first place. So for that reason I am mistrustful of this term!
On the other hand, the French use of the franglais 'rack' certainly seems to suggest they are indeed referring to some sort of rack system; what puzzles me most is the term "d'orgue" --- I don't know if this is merely referring to what is installed in the rack, but what would that be? We have a had a question before involving 'orgue' in a lighting context, maybe Asker would care to look this up in the glossaries to see if they might 'throw any light on the matter' (sorry!)
I suspect it may be something to do with a lighting console (often desk, hence pupitre), but the connection with an organ keyboard is common; maybe this is the lighting control rack that is usually associated with the actual operator's desk, though situated remotely from it? In that case, it would be 'dimmer rack' --- but since equivalent terms exist in French, it seems odd they should use this quirky one, UNLESS of course the text was written by someone rather non-technical; or, of course, that this is technicians' jargon!
HTH, anyway!