What is the difference between single phase and three phase power?

Single phase power supply is applied to an electric conductor / resister at 220 to 250 voltage for current to flow , where as 3 phase applied voltage is at 420 v to 450 v and in 3 phases ac waves will carry the current in a balance state but with time lag or lead time so overall power efficiency will be lower than 1 , over and above there will be more power loss and therefore its power factor with a better efficiency can be achieved around 0.9 .

Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution.It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads. A three-phase system is usually more economical than an equivalent single-phase or two-phase system at the same line to ground voltage because it uses less conductor material to transmit electrical power.

In simple terms single phase has 3 wires - 2 "hots" and a ground. Three phase has 4 wires - 3 "hots" and a ground.