I don't know about the rest of the world but line voltage in the US was to support the Edison incandescent light bulb and various motor designs. It seemed to start out at 110v AC at 60 hz and now has climbed to the standard 120v 60 hz (line to neutral) with a combined line to line of 240.
You will also see 115v and 117v referenced.
We use an arrangement with a center tapped 240v transformer, grounding the center tap. (120/240)
Once you get to 3 phase things are different with a center tapped wye (208/120v or 480/277) being the most common. There are also three different delta arrangements. It can be centertapped in one transformer (240/120/208 red leg), corner grounded (240/240/0) or ungrounded/impedance grounded but that is in special situations requiring more monitoring.
The corner grounded 3 phase service can be the most confusing since the equipment looks like single phase. I have only seen it in sewer lift pumps but there may be other applications out there.
