"To and fro" is an old fashioned or poetic way of saying "back and forth". "Fro" comes from dialects used in northern England and Scotland, into which it came from Norse (from "fra" meaning "from"). In standard English, "fro" is only used in the phrase "to and fro".

'Fro' is what is known as a 'fossil word'. It no longer exists as a usable word in the English language, but we know it once existed, meaning 'from' or 'away', because it is 'fossilised' in the single set phrase 'to and fro'. 'To and fro' has the same meaning as 'back and forth'.

In the region where I live in the USA it means back and forth. The expression to and fro is just another way of saying back an forth. Anyway that is he way it is where I live and the dialect here. Maybe it is different in other regions .

Its the same as back and forth or side to side.