"The voice of the internet — news before it happens"
Reddit is a very large news aggregator similar to Digg or Fark.com. Its structure is based around "subreddits", separate topic-specific aggregators which can be easily created.Birthplace and center of worship for the Dark Lord Inglip.It is more addictive than TV Tropes. Don't believe us? Here, try it for yourself. But don't say we didn't warn you. And whatever you do, do NOT piss off Reddit!
Astroturf: Reddit's founders, Alexis Ohanian and Steve Huffman, admitted to submitting links under various usernames when the site first launched to make it look like it there were more people using it than there actually were.
Exactly What It Says on the Tin: Novelty accounts, users who always post with a gimmick, generally have usernames that say exactly what they do. For example, Sure_Ill_Draw_That posts a drawing of whatever comment he replies to.
Getting Crap Past the Radar: After r/creepshots was banned, another similar subreddit, r/cshots sprang up with almost the exact same content, but claiming to be pictures shot by and for lesbian women. After that was banned r/candidfashionpolice showed up, again with almost identical surreptitious photos of young women, with commentary in the style of swishy gay men criticizing their taste in clothes, and even the same mods. It's still up as of this writing.
GIFT: The large userbase and loose moderation leads to many, many examples of the GIFT in action.
He-Man Woman Hater: Quite a few women (and men) on Reddit have complained about the site's skewed demographics (see There Are No Girls on the Internet) and outrageous sexism before. r/shitredditsays is the main hub for these complaints (although it's a subreddit that's widely accused of questionable behavior and comments in and of itself).
Honor Before Reason: The admins have refused to deal with some of the subreddits that promote illegal activity because it would violate their belief in freedom of speech, only deleting subreddits like r/jailbait after media pressure.
The most awesomely heartwarming of such counterattacks was when Something Awful released a "Redditbomb". Said bomb contained three core facts: Reddits contained child porn, the higher-ups defended the moderators of child porn sub-reddits, and that the upper elechons of the site tried to defend said child porn. It took multiple Redditbombs for the site to reluctantly ban child porn. fnord.
A counter-offensive against r/creepshots (taking lewd photographs of attractive women without their knowledge) on Tumblr that exposed the personal information of various creepshot posters.
Reddit was also a catalyst for the SOPA/PIPA protests.
The "SFW Porn" group of subreddits, which unanimously refer to "porn" in the Scenery Porn sense, i.e. pretty photos. Gets especially awkward with r/HumanPorn (which does occasionally have artful nudes) and r/AnimalPorn.
Poe's Law: The initial reaction to r/pyongyang is generally confusion over whether it's serious or not. On the one hand, the idea of a bastion of English-language pro-North Korea propaganda on one of the most mainstream American sites is preposterous. On the other hand, they're very dedicated to the charade.
Political Correctness Gone Mad: r/shitredditsays is widely known for its social justice and language policing. One look at the subreddit, and you should see why.
Rank Inflation: r/trees has a number scale to indicate how high the poster is. The problem is that unlike 420chan's number scale, it's subjective (i.e.  is the highest the poster has ever been, as opposed to adhering to certain objective symptoms). The r/trees FAQ acknowledges that most  posts are exaggerations. Some posters have suggested  or similar to actually refer to being that ridiculously high, but they are quickly shot down.
Serial Escalation: When one user posts a certain image, some others decide to post a new image trying to either one-up the previous one, or add [Fixed] to the replacement image. By the time a random reader notices, it's the sixth time they've created a new escalation for a theme, and they've become increasingly efficient about it.
Serious Business: Karma points. Dear Lord. "Power users" with extremely high karma tend to attract a Hatedomjust for having high karma.
Stealth Parody: One interpretation of r/shitredditsays is that its members talk about priveleged people, namely Straight Able-bodied Cisgender White Males (SAWCASMs) the way they talk about minorities on Reddit.
Troll: Many subreddits are full of these. It's usually best to assume that "I Am A" and "Ask Me Anything" posts are fake until proven otherwise; as you can imagine the idea is such a lure for trolls.
Trust Password: IamA and AMA posters are encouraged to verify their authenticity by submitting photos with a timestamp.
TV Tropes Will Ruin Your Life: It is considered slightly bad form to post a link to TV Tropes in a comment thread. Not that anyone there doesn't like us; just that once they get here they'll be stuck for the rest of the day.
Unknown Rival: Most of 4chan deeply despises Reddit, to the point where they've made hundreds of fake versions of Reddit's rage comics to troll themselves with. However, the hatred is generally one-sided.
Reddit has one of these with 9gag, Reddit having an entire sub-reddit devoted to complaining about 9gag, while most members of 9gag aren't even aware of that Reddit dislikes them.
Reddit has had a long-standing feud with Gawker, which boiled over in the violentacrez debacle.