A few more, including some more Rolex-centric ones:
ALS: A Lange & Sohne - high-end german watchmaker
AT: Omega Seamaster Aqua Terra
AP: Audemars Piguet - high-end Swiss watchmaker
Batman or BLNR: Rolex GMT-Master II with two-tone, blue and black, bezel (BLNR is french for 'bleu et noire' - blue and black)
BB: Tudor Black Bay
Bienne: City in which Omega has its headquarters; Members often suggest they're sending their watch "to Bienne" for service
BPH: Beats per hour - measure of a movement's frequency; arguably the higher the number, the higher the precision
CONUS: Continental United States (i.e. no Hawaii or Alaska). Used in sales form, as in "Shipping included within CONUS".
COSC - Controle Officiel Suisse des Chornometres (organization that certifies watches as "chronometres")
DJ: Rolex DateJust
DRSD: Double Red Sea-Dweller (Rolex)
Ed White: Omega Speedmaster 105.003, produced from 1963 to 1965. Last "pre-professional" Speedmaster without crown guards. Worn by Astronaut Ed White on NASA's first spacewalk.
EXPII or GMTII: Rolex Explorer II or Rolex GMT-Master II
Flip: A watch that's purchased and then sold for the express purpose of making a profit on the sale
GP: Girard-Perregaux - swiss watchmaker
GS: Grand Seiko
Hulk: Rolex Submariner with green bezel and green dial
JDM: Japanese domestic market - watch produced for Japanese market only
JLC: Jaeger-LeCoultre - well respected Swiss watchmaker
Kermit: Rolex Submariner with green bezel and black dial
MUT: JLC Master Ultra Thin
OF: OmegaForums
OP: Original poster (first member to post in a specific thread)
PAM: Officine Panerai
PO: Planet Ocean (as in Omega Seamaster Planet Ocean)
Pre-moon: Speedmaster made either 1) Prior to the moon landing being acknowledged on the caseback; or, 2) prior to the moon landing itself (pre-July 1969), depending on one's interpretation. I tend to favour the former.
Pre-Professional: Omega Speedmaster with straight lugs, without crown guards or "professional" on the dial, produced in the 1950's and early-mid 1960's.
RO: AP Royal Oak
RSC: Rolex Service Center
SD: Rolex Sea-Dweller
SEL: "Sold end links" - as opposed to "hollow end links".
SMP: Omega Seamaster Professional
Spa: OF for "watchmaker". As in, "Here's my Speedy, freshly back from the spa"
SubC: Rolex Submariner with ceramic bezel
SW: Straight Writing. An Omega Speedmaster 145.022-69 with "The First Watch Worn on the Moon" written straight across the caseback - the first example of a Speedmaster acknowledging the moon landing on the caseback
UG: Universal Geneve - much beloved, semi-defunct Swiss watch brand
105.012-65 CB - Speedmaster with a case produced by 'Le Centrale Boites' (rare example with slightly different case shape). Used due to unavailability of cases by Omega's regular case manufacturer Huguenin Freres
105.012-65 HF - Speedmaster with a case produced by 'Huguenin Freres'
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