The literally definition reads: "Indigenous or less commonly indigenous : of or relating to the earliest known inhabitants of a place and especially of a place that was colonized by a now-dominant group"
In most modern contexts it's used to refer to the diverse peoples that inhabited a land prior to European colonization.
In extension, here in Canada the Métis People (explicitly descendants of MIXED European and Indigenous ancestry) are recognized as an Indigenous group with unique language and cultural practices. They are by no means thought of as "pure bred" as you reductively tried to frame it.
The University of Alberta has an excellent, widely accoladed, and free MOOC on Indigenous Canada that I highly recommend you, and anyone else interested in learning more, consider taking: https://www.coursera.org/learn/indigenous-canada