I have done numerous Google searches, and come up with nothing remotely definitive for the reason for the name MUD given to MUD decks.
This quote is from an article written by one of the creators of the deck:
Now Mud didn't really have a name at that time; it was simply called "our Artifact deck" or "the Artifact deck" or it was just referred to as Mono-brown control. It wasn't until December-January when we first started making up names so it actually about five months after we created Mud.
In the train coming back from a Castricum tournament we figured it was about time to give our deck its own identity since decks like Stax and TnT were showing up in our environment. So we started making up more names using the word Mud; things like Muddy this and Muddy that. Can you believe it still took about three more days before I e-mailed Koen with this message?
You know what... How about 'Mud'?
So it's not MUD (it's not an acronym) and it is a reference to the brown (for the artifact frame) and slowing (for the lock) nature of the deck. That said, I still think other (non-Metalworker) Workshop decks can be called Mud, without confusion.
Generally, quite a few older deck names aren't really meaningful — they're a weird in-joke or just a random word someone pulled out of nowhere — and that tradition has been carried forward to the modern day in Legacy/Vintage as well. This is how you get the likes of Fruity Pebbles, Cephalid Breakfast, Team America (which is BUG, not red-white-blue), and Tinfins.
Sometimes there's a story behind it, but that story amounts to "I liked this reference" or "We had waffles at this restaurant the day before." About the most interesting story you're going to get from these is Boat Brew (created for a cruise; achieved massive hype quickly; lots of people today joke that it was an awful pile of a deck).
I've seen various backronyms for MUD, but really what you need to know is:
- MUD plays gobs of artifacts
- MUD decks are usually defined by Metalworker
- Artifacts (used to) have brown frames
The rest seems to be speculation and folk tales.
MUD Decks are typically decks that attempt to slow gameplay down drastically. You tend to see cards such as Tanglewire (Tapping permanents), Thorn of Amethyst (All non-creature spells cost 1 more to cast), and even Chalice of the Void on Zero or One (This prevents the powerful Moxen and Black Lotus cards in Vintage, Stops a lot of burn plays like Vexing Devil, Monastery Swiftspear, Lightning Bolt in Burn in any format Chalice is Legal). These decks capitalize on the slower gameplay caused and play threats that then become unstoppable. The signature name comes from an analogy, like wading through mud.
Hope this helps!
Yes, MUD is the name of the deck because of the brown frames artifacts used to have, the deck is mono-brown, and the prison/tax elements slow the game down. MUD was not intended to be an acronym, but Metalworker Urzas Destiny would be a great one. Chalice of the void, trinisphere, and thorn of amethyst slow the game down,and big robots like sundering titan/steel hellkite/wurmcoil engine/walking ballista can dominate the board. Big planeswalkers like ugin/karn can also exile threats and control the game. Fast mana like simian spirit guide/ metalworker/grim monolith/voltaic key/city of traitors/ancient tomb/vesuva cloning cloudpost + glimmerpost give you easy turn 1 chalice or thorn of amethyst,monolith into 3 mana which means you could also turn 1 trinisphere, or better, a turn 1 metalworker and do crazy things very fast.
MUD could be Mishra-Urza Deck, named after the two most famous artificers MTG has ever known & for not having a colour. From there, & over time as certain MUD decks became more prominent various names or iterations came about. Prior to Urza block they were known as Artifact decks as colored decks used few if any artifacts. With Urza block colored decks utilized artifacts heavily (esp. red, think Covetous Dragon, blue, think Tolarian Academy, Black w/ Memory Jar) thus MUD formed separately of Artifact decks which utilized colors along with the brown. From there, as brown decks began ascending as tier 1 tournament decks they began to differ thus their name differed to MUD (Metalworkers) and Shops (Mishra's Workshop) to delineate how mana was formed.