The expression 'Dreamtime' is most often used to refer to the 'time before time', or 'the time of the creation of all things', while 'Dreaming' is often used to refer to an individual's or group's set of beliefs or spirituality.
For instance, an Indigenous Australian might say that they have Kangaroo Dreaming, or Shark Dreaming, or Honey Ant Dreaming, or any combination of Dreamings pertinent to their 'country'. However, many Indigenous Australians also refer to the creation time as 'The Dreaming'.
What is certain is that 'Ancestor Spirits' came to Earth in human and other forms and the land, the plants and animals were given their form as we know them today.
These Spirits also established relationships between groups and individuals, (whether people or animals) and where they traveled across the land, or came to a halt, they created rivers, hills, etc., and there are often stories attached to these places.
Once their work was done, the Ancestor Spirits changed again; into animals or stars or hills or other objects. For Indigenous Australians, the past is still alive and vital today and will remain so into the future. The Ancestor Spirits and their powers have not gone, they are present in the forms into which they changed at the end of the 'Dreamtime' or 'Dreaming', as the stories tell.
The stories have been handed down through the ages and are an integral part of an Indigenous person's 'Dreaming'. (Dreamtime.net)
