Many large households with appliances that draw a lot of power (such as sheds, pool pumps, large air-conditioning units, bore pumps, heaters etc) will have 3-phase power.
If you take a close look at your electricity meter where your power comes into your property it will often have "Three Phase" or "Single Phase" written on it.
If this fails, then you can sometimes identify if you have single or three phase by your circuit breakers on your switchboard. If you have a three phase circuit breaker it means that you probably have three phase power.
The switches on three phase circuit breakers are usually three times the width of a single phase circuit breaker. They usually supply power to big appliances such as air conditioning units, sheds, electric hot water etc.