A trekkie is an extreme fan of Star Trek
, a sci-fi television franchise that has begat 6 TV shows, (The Original Series, The Animated Series, The Next Generation, Voyager, Deep Space 9, and Enterprise) and 11 movies, with 2 more in the making. Some of the more 'treking' trekkies attend star trek conventions, speak Klingon, and collect tons of Star Trek memorabilia. The not-as-intense trekkies are mere fans of extreme devotion, knowing phrases in Klingon and possibly Vulcan (though not fluent), know the actors playing the main roles of each series, and know all the names of the movies. Your standard Trekkie is probably addicted to Star Trek FanFiction. All trekkies have their own opinions on which series was best, but most agree that the two best were the Original Series and the Next Generation.
Wow, that girl is actually wearing a Star Trek Costume. She's a real trekkie.