Phase is a term used to describe alternating current. Phase explains the timing of the electron movements. Three-phase electricity is common worldwide because it is a cheaper and easier way to transmit electricity. But most homes only use single-phase electricity. Phase is a term used to describe one feature of alternating current. If wires are in phase it means that timing of the electron movement, back and forth, is the same. The electrons are in step or in time or in phase. Much of its efficiency is because there is always voltage in at least one wire. The idea of three phase power was discovered by Nikola Tesla (1856 -1943), a Serbian-born American engineer.
Three-phase power removes the need for a neutral or 'return path'. This is because joining the three phases together results in no overall current flow. Three-phase power is an arrangement that fits in very nicely with generator design. The 120° phase separation allows close to the optimum spacing and size of the copper conductors around the stator bore. The 3-phase generator is the cheapest form to make. Multiple phase generators are made for specific purposes, usually military, but they are expensive.