What shades do you include when you're thinking of "redheads?"?

I have colored my hair since i was around 12 years old, so not only has my hair changed a lot over the last 20 years, but I had also forgotten what it looked like in its natural state. I stopped coloring my hair a few years ago, and much to my surprise, found that I have a lot of natural red in my hair. I have always thought that my hair was very ash/cool and learning that my hair is this warm was a pleasant find. It also explains the pink/fair/freckled skin and green eyes that I always thought were just mismatched with my mousy hair. I think it would be classified as chestnut, it is medium brown with coppery undertones, that looks very red in the light (of course).

I made a joke recently, to my sister, that started “now that I’m a redhead,” and she stopped me dead in my statement and said “yeah, but you’re not a redhead.”

I’m inclined to agree with her, I was only joking because this is a recent discovery, but it made me start to think. How red is red enough to be a “redhead?” What shades of hair do you include and which do you think are too muted to really be called red? Is it about the ratio of blond/red or brown/red?