In Australia, the seasons are defined by grouping the calendar months in the following way:

Spring - the three transition months September, October and November.
Summer - the three hottest months December, January and February.
Autumn - the transition months March, April and May.
Winter - the three coldest months June, July and August.

These definitions reflect the lag in heating and cooling as the sun appears to move southward and northward across the equator. They are also useful for compiling and presenting climate-based statistics on time scales such as months and seasons.