LEGO Glossary of Terms, Shorthand and Jargon

AFOL: adult fan of LEGO
BL: see BrickLink
Blay or bley: a shortening of the term “bluish gray (or bluish grey)”. LEGO tweaked the color of dark gray and light gray pieces in the early 2000s, making them a more bluish color than before. Further reading: How to Distinguish “Gray” from “Bluish Gray” LEGO Pieces
BO: see Brick Owl
BOGO: buy one get one free
Bricklink: the largest unofficial LEGO only marketplace. It’s an eBay-like site for LEGO.
Brick Owl: a newer unofficial LEGO marketplace. It’s another eBay-like site for LEGO.
Clone: LEGO copycat products like Mega Bloks or KRE-O. Many LEGO purists use the term “clone” in a disparaging way. Secondarily, “clone” may also refer to a clone trooper from the Star Wars franchise.
Custom: an item compatible with LEGO that was not manufactured by LEGO. Some custom items incorporate modified LEGO pieces into their designs. Other custom items are unique. Quality of custom items varies since they are not official LEGO products. Custom items also fall into a legal gray area, so be very careful when dealing with custom items.
Dark Ages: A time gap in a fan’s passion for LEGO, typically spanning a few years or decades after childhood.
Fan Film: A fan-made movie inspired by an existing movie, television show or other pop culture source. Star Wars LEGO fan films are among the most popular fan-made LEGO productions.
FBTB: From Bricks to Bothans (a LEGO fan website)
Minifig: Short for “minifigure”, a minifig is a small LEGO figure
MISB: mint in sealed box or bag. Used primarily to refer to new LEGO sets with boxes in mint condition (without crunching, scratching or damage to the box).
MOC: my own creation (a LEGO project you have designed and built yourself without an instruction booklet)
Parting Out: The act of buying a LEGO set in order to sort and build with or sort and sell the pieces from the set.
TLG: The LEGO Group
SNOT: Studs Not On Top (LEGO studs). A LEGO building technique where to studs are positioned sideways or upside down in the project.
Stud: Studs are the bumps on top of bricks, plates and other LEGO pieces that allow pieces to interlock with others.
S@H: Shop at Home, the official LEGO online store
TRU: Toys ‘R Us, a major toy retailer that carries LEGO items.