Back in the day, I’m not sure that “nerd” was a complimentary word/label. Seems to be now it’s fine - and sometimes a real badge of honor!!!
Here is the google definition:
Nerd: a person who is extremely enthusiastic and knowledgeable about a particular subject, especially one of specialist or niche interest.
Keeping that definition in mind, what kind of nerd are you? Is it a badge of honor? Does it partly define you???
I’ll be thinking and posting my personal comments later. 
Although studious and a top student, I was not a nerd in HS, beauty school, or college, but became the definition of one in my career. I was a Unix operating systems (name your flavor) “guru.” I also spawned one.
It does not define me, but our son loves that his mother understands what he does (at some level) and can converse intelligently with his Cyber cohort. They all think I’m “cool.”
Today, I’m a CC nerd. That’s a thing, right?
In HS I was a band geek (which I think of as kind of the same think as “nerd”).
I’m the family research nerd now.
A math, puzzles and (computer) programming nerd 
And yes and yes to the other two questions.
History and Literary nerd. Love to go down those rabbit holes.
A “Lord of the Rings” nerd. I know far more than I should about the family tree’s of Elves.
Literary and policy nerd (though I prefer the term policy wonk). Yes, it’s a badge of honor that partly defines me. Civil discourse is a family pastime that goes on for hours when all the children are home. I know my poor spouse wishes we would all just pipe down.
Problem Solving nerd. For a long time I thought everyone could do it. After playing Lumosity for a few years I’ve found out that it’s my superpower (top 1/10th of 1 percent according to them), so I’ve started giving others more grace.
In my youth it was training animals (horses, dogs, cats). I thought everyone could do that too back in the day.
And now that I’m getting older I think all of it has morphed into Type B and Procrastination nerd. Everything that needs to get done gets done, on time, but my definition of need might differ from many other folk’s.
Every time I pick up a hobby I become a nerd in that area. So in the past I’ve been a photography nerd, woodworking nerd, and tennis nerd. Currently a kitchen knife nerd (which also makes me a tiny bit of a metallurgy nerd) and cooking nerd.
Word nerd here
My S’s were math nerds. They became, like DH, computer nerds. I was a band geek in HS too. Then (and still) am a science nerd.
I’m a watch nerd…but the community refers to it as “watch idiot savant” (WIS).
In engineering school (previously called a college technology) we referred to ourselves as Techers, proudly so. Or Geeks. At the time the dictionary said defined geek something like “circus performer who eats heads off snakes”…. but it was becoming a techie-nerd term.
I am my own blend of all the terms. But we tend to hang with a techie crowd (where hubby and I both worked before retirement), fine with that.
Hobby nerd!!
First, I’m a Geek, not a Nerd. So science geek, animal geek (not pets), fantasy (literary genre - get your mind out of the gutter!) geek, sci-fi geek (mostly movies and TV, less so books), and now I’ve started geeking out on geneology.
So do some people feel offended by “nerd”??
Not the intent of course and in fact, that’s why I started the post- because the definition is NOT negative - to me it’s favorable!
LOL - “nerd” makes me think of the SNL comedy sketches
I’m not offended; I think at one point decades ago it might have been derogatory but not so much anymore - it might possibly even be a badge of honor type of thing.
Geek vs nerd is an interesting comparison, I always had this vague sense that geek was slightly derogatory while nerd was not and that they meant slightly different things which I couldn’t articulate.
I found this explanation of the difference, but I think the terms are vague enough for everyone that many people would have different, equally valid definitions.
The last part crystallizes my own nerddom I think. For me it’s deep learning along with applying knowledge of a specific subject, moreso than just collecting things related to the subject.
“Both are dedicated to their subjects, and sometimes socially awkward. The distinction is that geeks are fans of their subjects, and nerds are practitioners of them.”
I don’t have enough drive and motivation to be a nerd, but I have interests in birds, native plants, rocks, etc. I keep a life list of birds and enjoy IDing plants on walks and hikes, but I don’t have a great deal of knowledge in any area.
Interesting. I agree that people have their own conclusions about both geek and nerd - some putting them in the same category.
I’m personally glad for “nerd” to not be considered derogatory as much as in the past!
If I think about it, “geek” leans more highly intellectual while “nerd” leans passionate about something but perhaps in a slightly awkward or non-traditional way?
Regardless, I don’t know that I can consider myself a nerd or geek about any one thing…