I call it a liquid line sight glass, that way it eliminates the possibility of a customer thinking I was inspecting a Lennox furnace when I was called out to look at a refrigeration problem.
I would also refer to it as the liquid line sight glass but for other reasons. Most if not all racks also have oil sight glasses on the resevoir/ and some have liquid bleed sight glass on the critical charge line, most compressors have oil pot sight glasses and oil sight glasses on the body/ this is not to be confused with the sight glass in the managers door when you go to get the bill signed.
In Australia we refer to it when talking to a customer as that little round brass thingy with the bloody window in it over there on the pipe.
Amongst us tradies though we call it the liquid line sight glass
Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002