Internet slang is slang that Internet users have created and used, often in instant messaging and forum discussions. They are frequently acronyms (often contain three letters), designed to save keystrokes in an attempt to speed up communication.
According to Harvard professor and conservative sociologist Steven Shapin, Internet Slang is an interpretation of language that people have found neccesary to create to confuse the "older" generation. 
List of Abbreviations
- 2: Substitution for to, too, and two.
- 4: Substitution for for and four.
- AFAICT: As far as I can tell.
- AFAIK: As far as I know.
- AFAIR: As far as I recall/remember.
- AFAIAW: As far as I am aware.
- AFK: Away from keyboard.
- ASL: A request for Age, Sex, and Location.
- ATM: At The Moment.
- BBL: be back later.
- BBIAB: be back in a bit.
- bewbs: breasts.
- BRB: Be Right Back.
- btw: By the way.
- ch00b: Person who acts like a n00b, but has skill levels or a kill/death ratio of someone who is considered 1337. Typically spends time bragging, flaming, and asking question he or she should know.
- D00d: L33tsp43k spelling of "dude".
- ftw: For the win.
- GDR: Grinning, Ducking and Running. Usually typed right after making a groan-inducing joke.
- g2g: got to go, gotta go.
- gg: Good game. Somtimes an 'a' is added to make gga: good game all.
- gl: Good luck.
- IANAL: Sometimes IANALB, "I am not a lawyer (but)" said right before (usually) poor legal advice.
- IIRC: If I remember correctly.
- IRL: In Real Life.
- IM: Abbreviation for Instant Messaging.
- IMHO In My Humble Opinion, or just "IMO" - In my opinion
- l8r: later.
- 1337 Leet. Usually means good, but some say it stands for Elite. Also the name for turning letters into numbers and symbols.
- LMAO Laughing My A** Off
- LOL: Laugh Out Loud.
- lvl: Level.
- m8: Mate.
- Newb Person is unskilled at whatever task they are trying to perform due to lack of experience.
- Noob Person is unskilled at whatever task they are trying to perform due to lack of experience and refuse to acknowledge their difficulty with the task.
- Omgwtfbbq is an internet slang term used in many MMORPG games like World of Warcraft. It is used as an expression of confusion and when someone asks an absurd newbie question. It is usually meant to be taken sarcastically. Although it can occasionally be used when someone is utterly confused by something that was said. Its various parts stand for, respectively, "Oh My G_d," "what the f___," and "barbecue," each of which can also appear individually, although "bbq," alone, is not actually considered internet slang.
- POS: Parent Over Shoulder. Usually used in IM conversations to alert the other participant of the presence of an adult/parent, and thus to avoid saying something inappropriate.
- Pwn: Defeat someone, misspelling of "own".
- Pwnt: If someone "pwns" you, you have been pwnt. Usually spelled with an 'ed' rather than a 't'.
- ROFL: Rolling On The Floor Laughing.
- Roflcopter: An extreme version of "rofl," or, "rolling on the floor laughing." Originated on World of Warcraft forums.
- ty: Thank You
- TMI: Too much information.
- U: Substitution for you.
- Ur: Substitution for your, you're, you are.
- WTF: exclamation of great bewilderment. Acronym for What The F***
- WYSIWYG: What you see is what you get, also a word processing editor type.
- ZOMG: An extreme version of "Oh my God!"
List of Terms
These are viewed by turning one's head sideways to the left.
- :-) is a smile - eventually known as a "smiley" and first posted 27 years ago by Scott E. Fahlman
- ;-) is a wink
- :-( is a frown
- XD is laughter
There are many variations on the above symbols (which are also known as 'emoticons'). Some symbols are called emoticons but are really examples of sideways ASCII art.