A Trekker, or more commonly Trekkie, is a self-described term for a die hard fan of the Star Trek science fiction franchise. Not all "trekkies" are created equal, however, with some having distinct preferences for The Original Series, The Next Generation, Deep Space Nine, or Voyager. Some are also fans of the Pocket Books tie-in novel franchise not unlike the Expanded Universe fandom of Star Wars.
Some Trekkers regularly attend Star Trek Conventions (called "cons"), and are sometimes bitter rivals of hard core Star Wars fans.
The term "Trekkie" is sometimes considered derogatory, perhaps because of a perceived parallel to the term "groupie." Some Star Trek enthusiasts prefer the term "Trekker," while others hold the latter term to be insufferably snobby and self-identify as "Trekkies."
There are many Star Trek fan clubs, the largest currently being STARFLEET International which has about 4,000 members.
There is a persistent stereotype that amongst Trekkies can be found speakers of the artificial Klingon language. The reality is less clear-cut, as some of its most fluent speakers are more language geeks than people obsessed with Star Trek. Most Trekkies have only the basic vocabulary of Klingon, like a few common words heard over the series innumerable times, but not Klingon's syntax or precise phonetics.
Trekkies have been parodied in several films including Galaxy Quest. William Shatner did a famous sketch on Saturday Night Live that also parodied Trekkies. There was once a pitch for a reality TV show featuring a group of "die hard" Trekkies/ers and 1 normal person, though it remains to be seen if such an episode will be aired.