AC voltage Supply

What is difference between Single phase and three phase ac supply?

Poly phase power

For simple questions such as this please try using Google or Wikipedia to find the answers for yourself, this information exists in exhausting detail on Wikipedia, read the article and then ask questions if there is something that confuses you.

Many users here love to help and answer questions, but it is good for those that ask a question to first attempt to do some basic research on their own.

Here is a link to the Wikipedia entry that defines what a poly phase AC system is (three phase is one type of poly phase system)