The people have described the single phase 120/240v system that is used in the USA, Canada, and Mexico, with the center-taped transformer. Japan uses a similar system but the voltage is lower: 100/200v. Most North America appliances work in Japan. Commercial and industrial systems in the USA run on three phase 208Y/120v or 480Y/277v. Canada uses higher voltage, typically 600/347v. These are all 60 Hz frequency.
Most of the rest of the world uses 50 Hz, three phase 240v phase-neutral ("ground") with 415v phase-phase. For residential use, just one 240v phase is used with neutral ('ground') so it is a two-wire system. If you are using appliances made for North America you must be "Very Careful" and know what you are doing. Motors will run 20% slower. To run equipment that requires both 120v and 240v, you need a special transformer. The higher voltages are more dangerous, especially the 400v phase-phase.
Three phase is very tricky and they don't teach all of it in electrical engineering school. I learned most of it in an Industrial Electricity course (tradesman apprentice class) at a community college, and some in Engineering courses at Purdue.
Most appliance from the US that can work 240V two hot wire, can work single phase 240v to neutral UK type. This is a common thing in the Caribbean Islands which uses the British system 230/400V 50Hz. You connect one leg to Live (hot), one Neutral and one Ground. Once you sure the operating voltage is 240V. This is also common in Bahamas.
In fact many welding machines are made overseas, and have a separate "Safety Ground" (Green/Yellow wire) and Blue and Brown hot/neutral wires in the power cord. I work in a hardware store that sells mostly imported tools and machinery including 240v welders.
Only a few North America appliances are 240v, like big heating appliances and big air conditioners. The only way to operate a 120v major appliance is a large transformer. The tourist converters for 1500 watt hair dryers break up the waveform by using electrical "trickery" similar to a lamp dimmer. The resulting waveform will destroy motors or electronics. Many small electronic devices, especially computer and cell phone chargers have a high tech "switching supply" that can handle any voltage from 100 volts to 250 volts at 50Hz, 60Hz, or even 400Hz. [Aircraft are 400 Hz.] These devices are labeled "100 to 240 Volts."
The only 'converter' is a BIG transformer.