The Reddit Glossary is a collection of specialized terms used particularly within @Reddit in order to save time and address specific situations. These phrases make communication more efficient for regular @Redditors but may leave casual users confused. The use of these terms tends to bleed into other community platforms as well.

Glossary

Alt - Alternative user account.
AMA - @Ask Me Anything (AMA); also a subreddit.
AMAA - Ask Me Almost Anything
At a [0-10] - "Being at a [0-10]" signifies the highness of the person that smoked marijuana with 0 being sober and 10 being blown into space. Mostly used in subreddits like/r/trees. E.g. "I wrote this at a solid [7]"
Benned - A perversion of the word "banned" used by SRS mods (see "SRS")
Brave or So Brave - A sarcastic expression used to dismiss a comment or patronize someone for falling in line with popular opinions.
Brony - A male fan of My Little Pony.
Cakeday - The day a user joined Reddit (like a birthday); it displays a small icon next to the username
Circlejerk - A group of people with similar beliefs that self-validate each other, suppress opposing opinions, do not consider that alternate opinions exist or consider themselves, their opinion, or their group exclusive/superior; derivatives include:/r/circlejerk: a parody subreddit that considers the majority of Reddit a circlejerk, Circlejerker(s): someone (or a group) from/r/circlejerk, or less commonly, a group that is a circlejerk.
@crosspost - Indicates that the post was also posted on another subreddit where OP recognized it; also stylized as "X-post"
Ctrl-F - Indicates that the user was searching for this specific reference in a thread
DAE - Does Anyone Else - An appeal to a common feeling/situation/dilemma; alsoa subreddit
@Default (Reddit) - The twenty subreddits that appear on the Front Page to users who are not logged in. Reddit users are automatically subscribed when they create a new account. These subreddits are chosen by having the highest activity on Reddit. You can find themhere (the first 20)
EDIT - Indicates someone has changed their comment after first posting it; usually followed by additional text, responses to subsequent comments, or explanations of why they edited their comment and what they changed
ELI5 - Explain like I'm 5 (years old) - A request to explain something in simple terms (alsoa subreddit)
Ent - Pot smoker. The term originally comes from the giant walking trees in Lord Of The Rings as trees are slang for pot; mostly used in/r/trees aka "home of the ents"
ETA - Edited to Add
F7U12 - Shorthand for FFFFFFFUUUUUUUUUUUU. Usually refers tothe popular subreddit focused on rage-comics
Fap – Masturbate
Flair - The images or text that appear next to usernames in certain subreddits; usually customizable
[FIXED] - A remix of an original post, often with the effort of making the post more relevant/close to the truth
Forever alone – Someone with no significant other (often abbreviated as SO) and (often) little-to-no social skills, and perhaps also simply unattractive
FTA - From The Article
FTFY - Fixed That For You; a small edit of a previous comment that changes the meaning in a (sometimes) fundamental and (almost always) humorous way
**FWP **- First World Problems; also a subreddit (r/firstworldproblems/) of complaints and problems that redditors find irrelevant
GW - Gone Wild; an NSFWsubreddit that features explicit or sexually suggestive photos of redditors
Hivemind - A collective; usually referring to the Reddit hivemind.
**HIFW **- How I Feel When; a subreddit for GIFs and pictures that convey emotions, much like MRW (r/HIFW)
IAMA - I Am A; alsoa subreddit in which noteworthy guests get interviewed by the Reddit community. It featured guests like President Obama, Snoop Dogg, Neil deGrasse Tyson, Scientists of the Mars Curiosity Rover Mission, and many more.
IANAL: I Am Not A Lawyer; usually used to preface legal advice and remind users that it might be better to seek counsel from an actual professional over a stranger on Reddit.
IMO - In My Opinion
IMHO - In My Humble (Honest) Opinion
IIRC - If I Recall (Remember) Correctly
ITT - In This Thread
@Karma - The point system Reddit uses. If people upvote your posts, you get link-karma; if they upvote one of your comments you get comment-karma. The opposite happens when they downvote. Self-posts (submissions in "text" mode) don't bring you karma. You can see a total of your karma on your overview page (when you click your username).
Karmawhore - A pejorative term for someone who reposts links (especially if they do it often), or posts links which pander to Reddit hivemind voting patterns in an effort to gain internet points; may also refer to a user who comments extremely frequently or in a pandering way
@lurker - a lurker is a @Redditor who reads and sometimes votes but does not post or comment. Some lurkers do so with accounts, some without.
Meta-subs or meta-reddits - Subreddits oriented around talking about Reddit itself. Subreddit content comes primarily (or exclusively) fromwww.reddit.com; there is/r/MetaHub,/r/TheoryOfReddit and more
MIC - More In Comments
Mod - Moderator of a subreddit; they have the power to remove comments and posts, among other things
MRA - Men's Rights Activist; member of a social movement that is focused on addressing discrimination against men in areas such as reproductive rights, divorce settlements, domestic violence laws, and sexual harassment laws. Members of this group have been known to fight with members of other social justice groups.
Neckbeard - A derogatory term used to describe the prototypical Reddit user. The term comes from the perceived poor hygiene of Redditors, and failure to shave the facial hair off of their necks for weeks and months at a time. Generally, someone is called a neckbeard when they (hypocritically) judge other people for their faults, but do not see any faults of their own.
Ninjaedit - Refers to the asterisk that indicates edited comments. If a comment is edited quickly enough after submission, the asterisk will not appear, removing any evidence that an edit ever happened, thus "ninjaedit". May also refer to comments that provide no indication that they were edited, despite the presence of an asterisk. These comments are looked down upon because they can make threads confusing to read.
Novelty account - An account usually used for humorous purposes, often repeating variations on a joke related to the name; e.g. user "Shittywatercolor" paints watercolors of various topics that arise in threads.
NSFW – Not Safe For Work; usually a warning of a link to a sexual image/video or gory content. People can also tag their posts to be NSFW by clicking "NSFW->yes" below the posted link.
NSFL – Not Safe For Life; usually a warning of a link to extreme gore.
@Original Content (OC) - Original Content; on Reddit, original content is king and reposted or old content is highly frowned upon. It's good etiquette to do a quick search on the site before sharing something, to avoid being embarrassed by unforgiving subreddit moderators.
OP - @Original Poster (OP); the person who made the submission that is now being commented upon
Orangered - The color of the envelope icon when you have an unread reply/message. To have an orangered is to have unread messages waiting.
Power user - A user with a high karma score whose username is recognizable to a large group of people on Reddit
Pun thread - A series of comments that make puns (often of lesser and lesser quality) that are related to a theme of the original post
Reddit switcharoo - An old comedy method and trope on Reddit, in which users will often facetiously put forward an interpretation of the original post that is coherent but not intended such as switching two elements in the post; e.g. someone posts a picture of a dog licking a person's face with the caption "I wasn't expecting that." The "switcharoo" might be someone commenting that "They also weren't expecting the human to react that way."
Reddiquette -Refers to the rules of Reddit, the rules of a specific subreddit, or less commonly to unwritten guidelines of conduct followed by typical Redditors.
Relevant username - Used when a comment has a coincidental relation to the name of the account that posted it
Repost - Posting an image or link that has already appeared on Reddit (usually the same subreddit) for the second (or more) time in an attempt to gain internet points. This usually comes up when the previous post was recent and well-received. The word repost is generally used to denote disapproval, and often sets off a debate on the validity of reposting in the context of user-voting.
RES -"Reddit Enhancement Suite"; browser add-on dedicated to improving the Reddit experience
RTFA - Read the Fucking Article
@Self-Promotion —
@Shadowban - A site-wide ban on a user that the user is not notified of. This is usually the result of breaking Reddit's rules. The user is unaware of the ban because their posts will still show up for them, but nobody else will see the user's activity. You can see if a person is shadowbanned if their overview page is an error page. People thinking they're falsely shadowbanned mayread this
Shitpost - A post that lacks any real value; usually ascribed to circlejerk posts or posts that are overly stupid, boring, sensationalistic, or lame
SO - Significant Other
Sockpuppet - Reddit specific definition: An alternate account (see "alt") used by a Redditor to speak in a voice other than that of the creator's recognized user name. Sockpuppets differ from ordinary alts in that they may be used to express controversial or negative opinions, rants, or trolls. In some cases, a sockpuppet may be shared amongst a group of users, for such purposes as moderation, vote brigading, or trolling. All alt's are not sockpuppets, but all sockpuppets are alts. A sockpuppet is basically a straw man.
Spamfilter - The system that filters out posts likely to be spam in subreddits; mods can choose to approve them or else they won't show up
SRD - Subreddit drama; usually refers to the subredditr/subredditdrama, but can also (very rarely) refer to the actual drama itself
SRS - Shit Reddit Says; a meta-sub centered around social justice issues and making fun of the behavior of Reddit users. Controversial opinions and moderation policies make SRS a hot spot for drama.
Sub - An individual @Subreddit
That's the joke or thatsthejoke.jpg - Indicates a commenter has just pointed out the humor in a joke, especially if the source of the humor is obvious
THIS - Indicates you agree with or want to draw attention to a comment
TIL - Today, I Learned; this stems from the subredditr/todayilearned, where redditors share fun facts they've learned today
@tl;dr - Too Long; Didn't Read; after a wall of text, a commenter may include a shorter description of what they wrote about, sometimes humorously. Sometimes inserted by another commentator to explain an article or previous comment.
Whoooosh. - Indicates that a joke has gone over someone's head
WIP - Work in Progress
**ಠ_ಠ **- An emoticon indicating extreme disapproval

References

Theory Of Reddit, reddit.com
The TL;DR Guide to Reddit Lingo, mashable.com
Learn how to speak Reddit, dailydot.com

Contexts

#reddit-lexicon (this memo is the @Root Memo)
#glossary (See: @Glossary of Glossaries)