DSF Posting Conventions
The DSF (now known as the DGF, or Diablo General Forum) has a very set way of etiquette.  Some regulars have been there for over two years, and certain things are expected of posters there.  I heartily recommend checking out Battle.Net 101 by Argus McFrugal at Freshman Diablo if you're a true newbie to the game.  It also has some tips on the DSF.

On the DSF, you'll see many posts with NT (no text) and NS (no strat) in the subjects.  Also used is OT (off topic).

Many newbies are afraid to ask questions for fear of being chastised for their lack of knowledge of the game, but it's an unfounded fear.  The regulars there are there to help, they've been doing it for a long time.  Ask your questions nicely and coherently and you'll be surprised by the wealth of information you can receive in return.

To prevent spamming, the forum requires a valid Blizzard CD-key to create a posting account.  Diablo was released before Blizzard began using CD-keys, so you must own a Blizzard game that has a CD-key in order to post.

About Nitpicking (aka "Nitting"): Nitpicking is making small corrections to posts to fix any errors or possible mix-ups.  It's very common.  Some people new to the forum can become annoyed by nitpicking and take offense to it, but that's because they haven't realized something: if a regular takes the time to nitpick your post, it means that he or she felt it was valuable enough to a) use a post up on it and b) read it through and comment on it.  It's good to be nitpicked!

Battle.Net
On Battle.Net, Blizzard Entertainment's free online multiplayer match-up service, it can be difficult to look up and get together with quality players.  Diablo 1 clients are banned from private channels now, so you can use a chat client can try looking in a psuedo-private channel named "Public Chat DSF-1" to find for games with DSF and Lurker Lounge regulars.

Jarulf's Guide
Also known as the Diablo Bible, the Book of Jarulf, or simply "The Guide," Jarulf's Guide to Diablo and Hellfire is the ultimate tome of technical knowledge of the inner workings of the game.  Constructed part by part over years by many contributors, Jarulf's Guide is the most accurate volume of information there is.  The Official Diablo Strategy Guide which nowadays comes with Diablo is flat out wrong in some parts, completely misguided in others, and is basically a really bad read if you want to know what's really going on in the game.  Get Jarulf's Guide, you won't regret it.  Most questions newbies ask can be easily answered by looking up the information in the Guide.  And everyone knows to always check your information with the Guide before making a detailed strategy post.  :-)

Landru
Landru was the DSF bot.  Bot being short for robot, it was an automated program to monitor the forum and provide five services:

• Tell the guild and site spammers to get lost,
• Count the number of posts by everyone on the forum to see who is posting the most,
• Rate what it considers to be "good" posts to recommend them to others,
• Occasionally post links to useful sites, and
• Crack the regulars up.

How did it crack the regulars up?  When it told a spammer to get lost (in its own polite way), spammers would sometimes tell the bot what they thought of it.  Of course, they were totally unaware it was a bot, which they'd have known if they ever actually bothered to read what they were spamming.

How did the bot decide what was good and bad?  Well, it had a list of keywords that it considered good, and keywords that it considered bad.  The list was much smaller than people think.  You would often see posters use words like c.heat or h.ack to avoid being caught for a bad word; however, those people didn't really understand how the bot worked, for it ignored those words (i.e., "cheat" and "hack") unless they were in the subject.

Who ran Landru?  The creator of the bot wishes to remain anonymous, and there were actually multiple versions of it being run on different machines.  I leave it as an exercise to the reader to try to figure out who ran Landru.  Unfortunately, Landru hasn't been seen in quite a long time, ever since Blizzard modified their forum scripts to make such a bot impossible.  R.I.P., Landru.

Mods
Mods (short for Modifications) started in 1998 with the Varaya and Khan mod (V&K) for Diablo and Hellfire.  The essential goal of mods is to enhance the game of Diablo by making it more difficult.  Therefore, they are not for newbies.  They are provided to return the challenge of the game back to old time players, and to renew the excitement of finding items and using spells never before seen.

Mods were once a hot topic on the DSF as people argued over their legitimacy, which had also greatly added to their exposure (and, frankly, got me to start playing the V&K mod).  Check out the mods page for a list of the more popular mods out there.

Variants
The Variants movement started in 1997 with the Beyond Naked Mage, or BNM.  The original BNMs, Woody and Hairy, took it upon themselves to find a way to make the game more challenging, especially for sorcerers.  They had no idea what they started...

Soon afterward, Woody founded Woody's Diablo Asylum, a site dedicated to informing people of the "Beyond Naked Way."  It caught on in the legit community like duped Obsidian Zodiacs did among cheaters, and dozens of players were having a blast collecting cursed equipment.  Things evolved from there, with new variants being thought of at a fast pace.  The current home for variants on the web is Realms Beyond Diablo, a joint site operated by variant lovers Charis and KingOfPain.

So what is a Variant?  To offer up a very short description, a Variant is a character who finds an interesting way to limit its capabilities.  Now, this goes beyond mere things such as "A warrior who can only use blades."  It's more along the lines of a rigorous set of ways of thought.  For instance, a BNM can only use cursed equipment, and actively seeks out equipment that's worse than what he's currently using.  Other BNM's become jealous of highly cursed items, for the worse your equipment is, the better the player you have to be to survive.

For more information on Variants, I heartily recommend Realms Beyond Diablo and The Sylvan Cliffs.