In 1967, science fiction editor Arthur W. Saha applied the term "trekkies" when he saw a few fans of the first season of Star Trek wearing pointy ears at the 25th World Science Fiction Convention, on the day Gene Roddenberry showed a print of "Amok Time" to the convention. Saha used the term in an interview with Pete Hamill that Hamill was conducting for TV Guide concerning the phenomenon of science fiction.

The Trekkie phenomenon did not catch on with general public consciousness until years after the show was cancelled in 1969. The show began syndication in reruns during the early 1970s and the first fan convention devoted to Star Trek opened in 1972 in New York.

Some Star Trek enthusiasts prefer the term "Trekkie", while some others self-identify as "Trekker". Self-identification as a "Trekkie" became even less popular after a famous national television parody in 1986; several self-described "Trekkers" were quoted as saying they "had a life" (contrasting themselves from "Trekkies").

In the 1991 TV show Star Trek: 25th Anniversary Special, Leonard Nimoy attempts to settle the issue by stating that the term 'Trekker' is the correct one.

In the documentary Trekkies, Kate Mulgrew stated that Trekkers are the ones "walking with us" while the Trekkies are the ones content to simply sit and watch Star Trek.

The issue is also shown in the film Trekkies 2, in which a Star Trek fan recounts a supposed incident during a Star Trek convention where Gene Roddenberry used the term "trekkies" to describe fans of the show, only to be corrected by a fan that stood up and yelled "Trekkers!" Gene Roddenberry allegedly responded with "No, it's 'Trekkies.' I should know — I invented the thing." Roddenberry has also allegedly used the term "Trekker" in interviews and personal appearances, arguably proving that he did in actual fact not consider either term to be the correct one. Generally, fans of film and television franchises make up their own nicknames, as with the "Browncoats" who are fans of the Firefly television series.

Star Trek fans who believe Star Trek: Deep Space Nine is the best series of the franchise adopted the title of Niner following the episode "Take Me Out to the Holosuite", in which Captain Benjamin Sisko formed a baseball team "The Niners".

There are many Star Trek fan clubs, among the largest currently being STARFLEET International and the International Federation of Trekkers.

Some Trekkies regularly attend Star Trek conventions (called "cons").

There is a persistent stereotype that amongst Trekkies there are many speakers of the constructed Klingon language. The reality is less clear-cut, as some of its most fluent speakers are more language aficionados than people obsessed with Star Trek. Most Trekkies have no more than a basic vocabulary of Klingon, perhaps consisting of a few common words heard innumerable times over the series, while not having much knowledge of Klingon's syntax or precise phonetics.

Trekies will listen to music from star trek, and make and listen to filk about it. Whilst more extreme trekkies will wear a full Trek uniform, most will only wear the ears, and the top or a star trek t-shirt, and the rest of their outfit will be exxencially normal.

Imfo save for the last paragraph from wikipedia, image from deviantart.

Just for the record, I don't mean to offend any 'Trekkers'. It's just that I use Trekkie, Wiki uses trekkie, the whole world uses trekkie. It just sounds better.