What about groups which haven't been colonized in any significant way? What about non-indigenous groups which have been colonized? It seems pretty arbitrary.

> What about groups which haven't been colonized in any significant way?

They are not generally considered indigenous. What about them?

> What about non-indigenous groups which have been colonized?

Examples of such groups?

> They are not generally considered indigenous. What about them?

I think there are examples, but it depends on how broad your definition of “colonized” is. The most extreme cases are the various isolated tribes of the world (of course, everything is interconnected, so a disingenuous person could argue that our impacts to the climate which affect their lifestyles constitute a kind of colonization, which is to say that disingenuous people like to stretch semantics).

> Examples of such groups

Virtually any non-indigenous people who have been conquered by an empire. The Irish are one of thousands of concrete examples.

>Examples of such groups?

Indians, Irish, many African countries, many SEA countries, etc

A often forgotten group are indigenous Austronesian Taiwanese people who were continuously displaced since the Qing dynasty but were subject to major cleanse and upheaval during the KMT retreat to Taiwan, leaving them to ~3% of the Taiwanese population.