Since this is the third of four full moons in this season, it is known as a blue moon. This rare calendar event only happens once every few years, giving rise to the term, “once in a blue moon.” There are normally only three full moons in each season of the year. But since full moons occur every 29.53 days, occasionally a season will contain 4 full moons. The extra full moon of the season is known as a blue moon. Blue moons occur on average once every 2.7 years.
In the northern hemisphere, this full moon was known by early Native American tribes as the Sturgeon Moon because the large sturgeon fish of the Great Lakes and other major lakes were more easily caught at this time of year. This moon has also been known as the Green Corn Moon and the Grain Moon.
In the southern hemisphere, we might call this the Full Kangaroo Moon. Kangaroos and wallabies have their joeys emerging from their safe and warm pouches as they start exploring their environment. They become a little more independent. This full moon could also be called The Full Growing Moon.
http://www.seasky.org/astronomy/astronomy-calendar-2021.html