It's a person that supports and believes in the U.S. constitution. It insures individual property rights, the rights to own the fruit of your own labor and the pursuit of happiness. It doesn't matter where a person migrates from. Most of our ancestors came from a different country and became U.S. citizens. They are Americans.
As an outsider, I see this as a good working definition of an American, US version.
I have a different idea of what an Australian is. We too are an immigrant nation with a population blended from people from every corner of the globe. Our constitution is not held to be sacred and we are much more communal in our approach to social structures although the Australian dream is to own your own home somewhere.
However, after a very long time spent travelling OS, as we refer to overseas countries, I came home questioning what an Australian really is, much as this thread does. We had spent 5 months on the move in the US, Canada and Britain. While questioning exactly what an Australian is, I discovered that I was definitely not any of the above. I had a completely different way of looking at the world.
Australians live on a continent that we don't have to share with anyone else. It is largely empty at the centre. We therefore tend to be outward looking, with an interest in the rest of the world. I have sometimes been asked on this forum why I bother posting on American issues. The answer is because I am interested in issues that arise in other parts of the world, particularly if I have visited that country in the past. Australians love to travel at home and abroad and we love vacation time. We work hard but expect a decent wage and decent conditions in return. We hate the tipping system of remuneration and expect workers to receive a livable basic rate with overtime and penalty rates for working unsociable hours.
Australia is still a young country and we tend not to value the past as much as older nations. We are not all that forward looking either. We tend to live in the present, unburdened by the past and sliding carelessly into the future. The expression "She'll be right, mate" sums up the nonchalance that exists most of the time but presented with an emergency or crisis we tend to snap into action, working together with strangers to rescue or help. We value volunteers who give themselves this way on an ongoing basis - surf lifesavers, volunteer firefighters, St John's ambulance and so on. Volunteerism is very important in Australian society and quite common.
All of the above is a description of a local mindset that has developed from the challenges of living on a large continent with an environment that was/is challenging to preconceived ideas of agriculture and animal husbandry and which could be very punishing in terms of drought, flood and fire. These challenges shaped the Australian psyche, drawing us closer to each other for survival in a seemingly hostile landscape. However, rather than being people of the land, we are mostly people of the suburbs, living in sprawling cities, paying off our own houses or units.
When we do turn our gaze away from the sea we see a magic land, with precious fauna and fauna and we realise that we have been blessed to have landed in this unique environment. Our first peoples believe that they are the protectors and custodians of this land and so they have been for millennia. Those of us who stem from immigrant stock have made many mistakes and have done much damage as we spread over the land in the name of progress, commerce and development. Realisation of this error hits hard and we are determined to fight for what is left, to protect the environment and the animals and plants that are found nowhere else on this earth.
Which brings me back to the idea of what the essential characteristics of an Australian are. I would say that first and foremost is an identification with the wide brown land of the interior and a passionate desire to care for and to protect it against further damage. This feeling is very strong in Aussies of very different political persuasions. It is not a left or right issue and new immigrants seem to pick up this feeling fairly quickly. We old Australians tend to be evangelistic on this issue and through the schools and youth organisations such as scouts etc we show their kids things what their parents have no idea about by taking them into the pockets of bushland that exist even in every capital city. Everything is protected - native plants may not be dug up or harvested for flowers, most native animals protected including dangerous ones such as snakes, sharks and crocs. If a possum takes up residence in your ceiling you cannot poison it. It has to be carefully removed by a specialist and released safely in an place where it is likely to survive. Snakes get the same treatment, at least in the cities.
Another essential characteristic is historical. Mateship is a concept that is diametrically opposed to competition and individualism. It has its roots in the gold fields of the nineteenth century and later on the battlefields of the Great War. Men discovered that survival depended on sticking together in small groups rather than going it alone. You stick with your mates through thick or thin. Today this characteristic lingers in our natural response to dire circumstances. It was apparent in New Orleans in the aftermath of Hurricane Katrina. There were a number of young Australians trapped in that blighted stadium and they immediately congregated and formed a defensive perimeter to protect each other against the violence that was occurring. They didn't know each other but they came together as Australians and came though the dangers together. It is the same response that Aussie POWs of the Japanese demonstrated. It is the very opposite of the US value of entrepreneurial competition and survival of the individual that was featured in the film King Rat.
I can't finish without referring to the Aussie tendency to irreverence. In Australia Jack has long considered himself as good as his master. If someone seems to be getting too full of himself, too puffed up with her own importance, there will be a swift take down by others. We call it the tall poppy syndrome and you had better stay humble if you don't want a lesson in humility. I think this is why Australians look aghast at characters like the Kardashians and Donald Trump who are shameless self promoters. On the other hand we respect figures like Queen Elizabeth for her long life of duty and we condemn anyone who thinks it smart to disrespect her person. You can joke about her but it must be gentle or we won't laugh.
None of the above are unique to Australians but they are strong in us.