1ST ED: First Edition (books)
AB: Aurora Borealis (used in jewelry descriptions)
ACC: Accumulation (postage stamps)
ACEO: Art Cards, Editions and Originals (miniature paintings on 3.5 inch by 2.5 inch cards)  See also OSWOA and SFA
ACL: Applied Color Label (bottles)
ADV: Adventure (Books / Movies)
AIR: Air Mail (postage stamps)
API:  Application programming interface
ARC: Advance reader's copy
ATC: Artist trading card (miniature artwork measuring 2.5 x 3.5 inches as per ACEO)
AU: Australian dollars (see currency exchange site)
AUTO: Autographed
AUTH:  "Not quite authentic"
B&W: Black and white
BB: Beanie Babies
BC: Back cover;  British Columbia, Canada; blister card
BC ED: Book Club Edition (in books)
BCE:  Book Club Edition (in books)
BETAMAX: First video tape format (still used in Ghana & West Africa)
BIN: Buy It Now
BKLT: Booklet
BLK: Block (postage stamps)
BMC: Book of the Month Club Edition
BNIB: Brand New In Box
BNWT: Brand New With Tags
BOMC: Book of the Month Club Edition
BP: Blister pack; booklet pane (postage stamps)
BTS: Back to School
C: Carat (a unit of weight for precious stones & pearls equal to 200 mg)
CDF: Customs Declaration Form (postage stamps)
COA: Certificate of Authenticity (also stands for Coat of Arms)
COD: Cash on delivery
COMP: Composition Doll
CONUS: Continental US
CTB: Coffee table book
CDS: Circular Date Stamp (postage stamps)
CTO: Cancelled to Order (postage stamps)
CZ: Cubic zirconia (NOT a diamond)
DEF: Definitives (postage stamps)
DL: Download (frequently used for Digital Downloads)
DOA:  Dead on Arrival
DLX: deluxe
EAPG: Early American pattern glass
ED: Edition
ETA : Estimated Time of Arrival
EURO: European Union Currency
EUC: Excellent used condition
EXC: Excellent
EXLIB:  Formerly a library book
F:  Fair or Fine condition [ask the seller; don't presume]
FAQ:  A list of frequently asked questions with answers
FAUX: Not a genuine item (as in faux pearl)
FB: Feedback
FC: Fine condition
FCM: First class mail
FDC: First Day Cover (postage stamps)
FLB: Former Library Book
FNH: Family Name History
FOB: Freight on board
FR: Former Rental (VHS tapes or DVDs)
FS: Factory sealed
FS: Full Screen Format on DVD
FUBAR: Fouled Up Beyond All Recognition
FVF: Final Value Fee
FYI: For your information
G: Good condition (also GC)
GBP: Great Britain Pounds (pounds sterling) (see currency exchange site)
GF: Gold filled
GP: Gold plate
GSP: Gold sterling plate
GU: Gently Used. Item that has been used but shows little wear, accompanied by explanation of wear
HB: Hardback book
HC: Hardcover book
HC DJ: Hardcover Book with Dust Jacket
HCTS:  Here Comes the Stork (seller group)
HP: Home page, Hand Painted, Hewlett Packard
HP: Hard Plastic Doll
HS: Hand Stamp (postage stamps)
HTF: Hard to find
HTML: HyperText Markup Language; the language used to create Web pages
IBC: Inside back cover
IE: Internet Explorer
IFC: Inside front cover
INIT: Initials
INR: Item Not Received
ISP: Internet Service Provider - a company that gives you access to the Internet
JPG: Preferred file format for pictures on eBay (from the Joint Photographic Experts Group standard, pronounced "Jay-Peg")
K: Karat (1/24th part of pure gold)
KWS:  KeyWord Spam
L: Large (also used, Lg or  Lrg)
LCD: Liquid Crystal Display
LE: Limited edition
LED: Light Emitting Diode
LN: Like new
LP: Long playing (33 rpm record album)
LP: Large print (books/magazines)
LS: Long sleeves (in clothing)
LSASE: Large self addressed stamped envelope
LTBX: Letterbox. Video format that recreates a widescreen image
LTD: Limited edition
M: Medium (also used: Md or Med)
MCM: Mid-Century Modern
MH: Mint hinged (condition of postage stamps)
MIB: Mint in box
MIBP: Mint in blister pack
MIJ: Made in Japan
MIMB: Mint in mint box
MIMP: Mint in mint package
MIOJ: Made in Occupied Japan
MIOP: Mint in open package
MIP: Mint in package
MIU: Made in USA
MM: Media Mail Shipping by USPS
MNB: Mint no box
MNH: Mint never/not hinged (condition of postage stamps)
MNT: Mint. In perfect condition (a subjective term)
MOC: Mint on card
MOMC: Mint on mint card
MONMC: Mint on near mint card
MOP: Mother-of-Pearl
MOTU: Masters of the Universe (He-Man), or Mark Of The Unicorn, an audio equipment manufacturer
MP: Military Post (postage stamps)
MPRS: My Poupette Recommended Seller (seller group)
MTG: Magic the Gathering Card Game
MWBMT: Mint with both mint tags
MWBT: Mint with both tags
MWMT: Mint with mint tags
MYO or M.Y.O.:  Million years old
NARU: Not a registered user (or suspended user)
NDSR: No dents, scratches, or rust (condition of tins)
NBB:  Non-binding bid (real estate category term)
NBW: Never been worn
NC: No cover
ND: No date
NIB: New in box; No international bidders
NIL:  Not in Line (not a standard product of the manufacturer; a special issue)
NIMSB: New in manufacturer's sealed box
NIP: New in package
NM: Near mint
NOS: New Old Stock
NP: Not packaged
NPB: Non-paying bidder
NR: No reserve price for an auction-style listing
NRFB: Never removed from box
NTSC: Video & DVD format used in US, Canada, Mexico, the Phillipines, the Caribbean, most of South America excluding Brazil & Argentina, Taiwan, South Korea, Burma, & Cambodia (not PAL or SECAM)
NWOT: New without tags
NWT: New with tags
OEM: Original equipment manufacturer
OOAK: One of a Kind
OOP: Out of print
OPT: Overprinted (postage stamps)
OSWOA®:  Original Small Work of Art measuring 6 x 4 inches, so as to fit in a standard 6 x 4 or 4 x 6 inches photo album sleeve.  See also ACEO and SFA.
OSFA:  One Size Fits All
PAL: Video & DVD format used in the UK, Australia, Germany, Spain, Portugal, Italy, Belgium, Holland, Hong Kong, Scandinavia, Poland, China, India, Pakistan, Turkey,  most of Africa, and the Middle East - it is the DOMINANT format in the world (not NTSC or SECAM)
PB: Paperback book
PC: Poor condition; postcard
PF: Proof (coin)
PM: Priority Mail shipping method of USPS
PP: Parcel Post shipping method of USPS; PayPal
RC: Reader's copy
Reg: Registered (postage stamps)
RET: Retired
REV. ED.: Revised edition (books)
ROPS: Rollover Protective Structure; a cab or frame that provides a safe environment for the tractor operator in the event of a rollover
RPPC: Real Photo Postcard (not an illustration)
RS: Rhinestone(s)
S:  Small (also used, Sm or Sml)
SAIS: Sold As Is
SASE: Self addressed stamped envelope
S/B: Stockbook (postage stamps)
SC: Slight crease (tags, books, magazines)
SC: Softcover book
SF: Science-fiction
SFA: Small format art (any artwork measuring under 14 inches).  See also ACEO and OSWA.
SCO: Second chance offer
SCR: Scratch
SECAM: Video & DVD format used in France, Russia, Eastern Europe, & some parts of the Middle East (not PAL or NTSC)
S/H; SH, S&H:  Shipping and handling
SHI: Shipping, handling, and insurance
Sig: Signature
SM:  Selling Manager
SMP:  Selling Manager Pro
SMI: Safeguarding Member IDs
SNAD: Significantly not as described
SNAFU: Situation Normal, All Fouled Up
SO: Sold Out
S/O: Sold out
S/P: Salt and pepper (shakers); silverplate (flatware)
SS: Short sleeves (in clothing)
SS: single sheet (postage stamps)
SS: Stainless steel
SS or 925: Sterling Silver
SS: Still sealed
STER: Sterling
SW: Slight wear
SZ: Size
SYI: Sell Your Item form
TA: Trading Assistant
TE: Trade Edition (typically smaller than standard book)
TIA: Thanks in advance
TKO: Account TaKeOver
TL: Turbo Lister
TM: Trademark
TOS: Terms of sale; terms of service; The Original Series (Star Trek)
UNC: Uncirculated (coins)
UPI: Unpaid Item
UPS: United Parcel Service
URL: Uniform Resource Locator. The address that identifies a Web site (such as www.ebay.com).
USPS: United States Postal Service
V2000: also known as Video Compact Cassette, or VCC - began in 1979 and ended in 1988 (marketed exclusively in Europe)
VBO: Vintage Blow Out Sale: 4 times a year Vintage Clothing Sellers place items on ebay at amazing prices of 19.99 or less with Buy it now.
VeRO:  Verified Rights Owner
VF: Very fine condition
VG or VGC: Very good condition
VHTF: Very hard to find
VR: Very rare
W / : With
WBN:  Winning bidder notification
WMK: Watermark (postage stamps)
WOB: Writing on back
WOF: Writing on front
WS: Widescreen in DVD (same as Letterbox)
WYSIWYG: What you see is what you get
XL: Extra large
XS: Extra small
XXL or 2XL: Extra extra large or 22/24 W
XXXL or 3XL: Extra extra extra large or 26/28 W
YFD:   Yard Fard Days (seller group)

See also abbreviations/acronyms used in eBay's message areas

(This Guide was an eBayWiki article created by several eBaysians and is preserved here because the information is worth keeping.  If you have additions, please submit them to me.)