xkcd is a webcomic created by Randall Munroe, a former contractor for NASA. It calls itself "a webcomic of romance, sarcasm, math, and language." The site states there is no particular meaning to the name, that it is simply a "treasured and carefully-guarded point in the space of four-character strings."
The subjects of the comics themselves vary. Some are statements on life and love (some love strips are simply art with poetry), and some are mathematical or scientific in-jokes. Some strips feature simple humor or pop-culture references. Although known for its crudely drawn cast of oddball stick figures, the comic occasionally features landscapes, intricate mathematical patterns such as fractals (for example, strip #17 "What If" shows an Apollonian gasket), or imitations of the style of other cartoonists (as during "parody week"). Occasionally, realism is featured.
The comic is available under the Creative Commons Attribution-NonCommercial 2.5 License. New comics are added three times a week, every Monday, Wednesday, and Friday, at midnight although so far they have been updated every weekday on three occasions: parody week, the five-part 'Choices' series and the 1337 series.
The comic began in September 2005 when Munroe decided to scan doodles from his school notebooks and put them on his webpage. Eventually the comic was changed into a standalone website, where Munroe started selling t-shirts based on the comic. He currently "works on the comic full time," making xkcd a self-sufficient webcomic.
In May 2007, the comic caught the attention of many by depicting online communities in geographic form. Various websites were drawn as continents, each sized according to their relative popularity and located according to their general subject matter. This put xkcd at number two on The Post-Standard's "The new hotness" list.
xkcd is not an initialism, and Munroe attaches no meaning to the name, except in a joking manner within the comic. He claims that the name was originally a screen name, which he selected as a combination of letters that would be meaningless, as well as phonetically unpronounceable.
On September 23, 2007, hundreds of people gathered at coordinates mentioned in a strip: 42.39561 -71.13051. Fans converged on a park in North Cambridge, Massachusetts, where the strip's author appeared; among his comments: "Maybe wanting something does make it real," reversing the conclusion in the last frame of the same strip.
In October of 2007, a group of researchers at University of Southern California Information Sciences Institute conducted a census of the internet and said that their data presentation was inspired by an xkcd comic.
On April Fool's Day 2008, xkcd was part of a three-webcomic prank involving Dinosaur Comics and Questionable Content wherein each comic's URL displayed another comic's web page: questionablecontent.net displayed the Dinosaur Comics website, qwantz.com (the Dinosaur Comics website) displayed xkcd, and xkcd.com displayed the Questionable Content website. The prank was orchestrated by Randall Munroe, as Jeph Jacques announced on his website on April 2nd:
Recurring items Edit
While there is no specific storyline to the comic, there are some recurring themes and characters, many of which are touched on in a comic parody of Discovery Channel's I Love the World commercial.
A large number of the strips are mathematics or computer science jokes. These jokes often feature university-level subjects, although many are written in such a way that a clear understanding of the subject is not usually required to get the punchline. Romance is another subject often visited in the comic, with many strips not intended to be humorous. Many of the female characters display conventionally masculine attitudes and interests. xkcd frequently makes reference to Munroe's "obsession" with potential raptor attacks, the game Guitar Hero, characters making out with themselves, and many "your mom" jokes. There have also been several strips featuring "Red Spiders", zeppelins, Joss Whedon's short-lived series Firefly, Ender's Game and Wikipedia. Each comic has a tooltip, specified using the title attribute in HTML. The text usually contains an afterthought or annotation related to that day's comic. There are also many strips depicting "My Hobby", usually depicting the non-descript narrator character describing some type of humorous or quirky behavior often involving language games.
- A man in a hat who looks like a normal stick-figure xkcd character, but for the addition of his trademark black hat. Referring to himself as a "Classhole" (classy asshole), he is intolerant of internet newbishness. He does not shy from pointing out the foibles in others and has at times used extreme violence in order to emphasize a point.   He is closely based on the character Aram from the Men In Hats webcomic. In the January 30, 2008 comic, his hat was taken by a woman, who is, to date, the only person ever to foil one of his schemes. On April 2, 2008, in a Russian submarine he managed to track down the woman and take his hat back. As of June 6, 2008, they have entered a "relationship."
- A boy in a barrel has appeared in 5 strips. Unlike most other characters, he is not a stick figure. He was repeatedly seen inside a barrel, floating in a large body of water. The boy in the barrel was one of many doodles in the older comics, but as of July 2008, has not been seen since comic #31.
- Another set of recurring characters is the nihilist and the existentialist, recognizable by their hats; the existentialist wears a beret and the nihilist wears a white top hat (or no hat at all). Until comic #434, they had only been seen together, never separately. They can first be seen in the "Nihilism" comic,  and again in "Kayak", "Hypotheticals" and "Dignified". The existentialist can be seen with a girl in the first frame of the strip "xkcd Goes to the Airport" Recently, the existentialist can be seen in the 3rd and 22nd frames of "xkcd Loves the Discovery Channel".
- Munroe is often a character himself, either identified explicitly as such onscreen or narrating scenes occupied by unnamed characters or no on-screen characters at all.
- Fictionalised versions of well known real-life figures in the computing community sometimes appear, such as free software advocates Richard Stallman  and Cory Doctorow. 
- Mrs. Roberts was a main character in the "1337" series, and has appeared in other comics along with her children, "Robert'); DROP TABLE Students;--" aka "Little Bobby Tables," (a reference to SQL injection)  and "Help I'm Trapped In A Driver's License Factory Elaine Roberts", the protagonist of the "1337" series. Elaine's first name is a reference to "Pi Equals."
Life imitates xkcdEdit
On several occasions, fans have been motivated by Munroe's comics to carry out, in real life, the subject of a particular drawing or sketch. Some notable examples include:
- Richard Stallman was sent a katana and was confronted by students dressed as ninjas before speaking at the Yale Political Union – inspired by "Open Source"
- When Cory Doctorow won the 2007 EFF Pioneer Award, the presenters gave him a red cape, goggles and a balloon – inspired by "Blagofaire"
- xkcd readers sneaking chess boards onto roller coasters – inspired by "Chess Photo"
- An xkcd reader created a "MBR Love Note" installation program – inspired by "Fight"
- Munroe himself solicited contributions from his readers of people playing electric guitars while in the shower on wetriffs.com after posting the comic "Rule 34", in which a character registers that domain.
- Many xkcd readers headed up to random latitude/longitude locations calculated by the geohashing algorithm described in "Geohashing".
- Munroe, the creator, has mentioned in two of his "blag" entries, that he has a ball pit set up in his apartment, much like in the strip Grownups
- Probably one of the easiest xkcd pranks that readers have done is posting notes next to elevator buttons saying either "zeppelin" or "love". Inspired by Elevator
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