When all else fails, you call Mousa the 14, that one ranting geek.
call me a semantics freak, but I coulda swore that these terms had specific definitions, but that could just be me. More a long time people have used the words interchangeably to simply mean "Socially inept guys we mainstream people don't like because they have non-mainstream interests, dress casually, act weird, and aren't particularly attractive."
Then why have two words? Words that are different yet supposedly mean the same or similar thing? and I'm sure people have their own personal mental dictionaries that give each of these words a specific term. even my mainstay, TvTropes.org, has separate definitions for each.
The distinction is subtle, too subtle for anybody to really care so they ignore it. However I believe that from all I've heard and read I can glean some sort of distinction.
I realize this may be futile. I mean, XKCD is laughing at me right now for it. But the alt text proves to me that even the XKCD guy has a version of it and in fact mine is quite similar. So without further ado I present the definitions.
NERD: A socially inadequate person who is noted not only for their poor social skills or lack of caring of mainstream interests and styles, but for their intelligence, display of said intelligence, and deep knowledge of a wide variety of fields or a specified field. The big difference between a geek and a nerd is that a Nerd's brilliance is usually within academic pursuits. They are Science geeks, math geeks, computer geeks. If it is an academic field with real life applications or at least has a real field of study and you are intellectually vested in it, you are a nerd.
GEEK: A subset of hobbyist, people who have an deep interest in traditionally non-mainstream subjects that are often considered childish in nature. Similar to the Nerd, they are usually socially inadequate and brilliant. Unlike the nerd, their brilliance tends to be dedicated to their specific hobby. Usual interests of Geeks fall under Science-Fiction and Fantasy Genres spanning all mediums. Another aspect of Geeks as defined by The Game Overthinker in his video on continuity found here. the short and paraphrased version is this: "Geeks glean fun from turning something that is already fun into work" such as playing video games competitively, Stop Having Fun Guys, or collecting the entirety of the Marvel universe's comics to "keep the continuity straight".
Geeks follow this mantra "(Insert Hobby here), My Anti-Drug: Because Crack is Cheaper"
Agree with me, don't agree with me. I think I'm right, but I'm just that one ranting geek among millions. I doubt I'm wrong but I dare thou to challenge me.
Though it does seem strange that some, including myself, are arguing over the semantics of an insult pointed in our general direction.
-Good Bye, Good Luck, and Imagination Is Your Greatest Power.
Mousa The 14