Regarding the names of colours in my posts. In an attempt to be completist, I list both of the common names. [BL] refers to the community name used by the website BrickLink and [TLG] refers to the official name used by The Lego Group. I know it looks ugly. Sorry. Where BL and TLG use the same name I make no annotation.
And as for those confusing piece numbering systems I include - refer to Element ID and Design ID.
AFOLAdult Fan Of LEGO®. The standard acronym used by the community to describe themselves, used since the early days of online LEGO community began to form. This thread is purported to be its coining. (Thanks to DaveE for the great link. Plenty more on his amazing AFOL History Project.)
TFOLs (Teen Fans of LEGO) are another distinct group of people who fall outside The LEGO Group's main focus since probably most kids stop playing with LEGO in their teens. Some people just say FOLs, to encompass both teens and adults, but I'm not in the habit, so TFOLs can certainly consider themselves included when I say AFOLs!
BleyBluish Grey, known as Stone Grey within LEGO®. In 2004, LEGO changed the shade of light and dark grey LEGO to be a little bluish instead of greenish. They did it in all innocence never imagining anyone would care or even notice... but there was a massive outcry from the AFOL community! 'Bley' was a derogatory term they coined and it has stuck, though perhaps now used with more affection with the fullness of time.
ConstractionLEGO®'s internal name for buildable figure ranges such as Bionicle and HERO Factory.
Conversion setThe set that brought an adult out of their Dark Age, making them an AFOL.
DalekSNOT brick that's like the regular 1X1 brick but with Apollo studs on all four sides as well as the top . It is a greatly-loved part amongst AFOLs and has many nicknames, I think most the common one is the Travis brick but I prefer this British nickname given due to its vague resemblance to the Daleks, an alien monster from Doctor Who. Of all 1X1 bricks, the Dalek is the costliest that TLG make.
Dark AgesThe period from when you stopped building with LEGO® as a child and then started again.
Design IDThe LEGO® Group assign a reference number to each different part. You can find them somewhere on the underside of every LEGO® piece (except old ones). These are called the Design ID, but in the community they are usually just called the part number. You can search Brickset or Bricklink using these numbers to see how many elements come in that part (i.e. how many different colours). You can also enter it into LEGO's Pick a Brick site to see if they sell it individually.
See also Element ID below.
Design LabA department of TLG in Billund who are responsible for the design of parts and are the 'custodians' of the System. They ensure the features of parts are standardised across the whole inventory and that the suitable principles of LEGO building are maintained. The full details of these principles are largely a guarded trade secret but perhaps the most important principles that we mere mortals know of are not to allow connections that place stress on parts (known as illegal connections) and to enable stable building experiences from the ground upwards (literally). Children unknowingly flaunt these principles of course, whereas AFOLs do it knowingly and often gleefully. Both children and adults cry when their model falls to bits because they didn't follow the principles. Lesson: Trust the System. The System is your friend.
Element IDAs well as every part having a number, The LEGO® Group also assign a reference number to each different element. Remember, an element is unique in colour as well as shape, so there are squintillions of elements! You can find them in every LEGO® instruction manual (except old ones) at the end where the inventory is listed. These are called the Element ID, but the term is not used much (or understood well) amongst AFOLs. Nevetheless you can use them to search on Brickset and Bricklink - although, Bricklink will take you to the part page instead and a message near the top will let you know what colour matches the Element ID you searched for. You can also enter it into LEGO's Pick a Brick site to see if they sell it individually.
See also Design ID above.
ElementsThe official name for each unique LEGO® part. An element is not just the shape of the part but also the colour; so two identically shaped parts in different colours are considered different elements.
Erlingunusual aspects to its geometry and the anti-stud hole on its back side. It was designed in 1979 by a chap called Erling Dideriksen.
GreeblesGreebling is a term used primarily in the movie industry to refer to the little bits of stuff applied to the exterior of a spaceship to make it look cool. The term can be used more widely than that though - Wikipedia defines it as "fine detailing added to the surface of a larger object that makes it appear more complex, and therefore more visually interesting" - but in the FOL world, spaceships are probably the most common type of MOC where greebles are used.
Illegal connectionsOne of the great joys of building LEGO® is connecting the pieces in ways that set instructions wouldn't suggest. We've all stuck a plate between the studs of a brick, right? Actually, even LEGO used to do that one decades ago in their set instructions. But this is an example of what The LEGO Group now term illegal connections, because it places stress on the elements (however minute) and/or is an unstable method of building. These connections are not entirely known outside of TLG but this (now a little old) presentation by Designer Jamie Berard explains many. Children, TFOLs and AFOLs alike are terribly disrespectful of such LEGO 'laws', as we are not a responsible toy company. As such we flagrantly enjoy disobeying them and even boast of illegal connections we've discovered. Then cry when we knock the model lightly and it shatters into a thousand elements.
Legal connectionsSee Illegal connections.
LUGLEGO User Group. Fan clubs around the globe are known as LUGs and they are officially supported by The LEGO Group, so search for one near you and join up! (Not to be confused with the term LUG which refers to Lotus User Group - this is especially important if you follow Warren Elsmore on Twitter.)
Minifigs and Minifig ScaleLEGO® Minifigures. The little LEGO people, introduced in the '70s. Initially they had no posable arms or legs and no facial expressions, but that was soon changed to the bendy little folk we know and love today.
Something built in 'minifig scale' means all the buildings, cars etc are built at the same scale to a minifig. The human:minifig ratio is very vague due to the strange shape of minifigs, so two minifig scale models might not match. It is about 1:40 to 1:50.
MOCMy Own Creation. A model built by a fan.
ModularsThis is a series of sets aimed primarily at adult builders and collectors, each consisting of a large building with removable storeys. The buildings all connect to build a street in minifig scale. One building has been released each year since 2007, when LEGO® Designer and former AFOL Jamie Berard began the series. They are beloved by AFOLs thanks to their size, exclusivity, interesting and challenging building techniques, and of course rare parts. The name Modulars comes from the fact that you can add extra storeys to your building by buying more pieces to replicate floors. A set also usually considered a Modular is 10190 Market Street which was designed by Dutch AFOL Eric Brok and released by LEGO in 2007. Also available is a set of the first five Modular buildings in microscale - 10230 Mini Modulars, also designed by Jamie Berard.
MouldsMoulds are the huge expensive metal moulds LEGO® inject molten plastic into to create elements. They are incredibly sophisticated and expensive lumps of metal!
NCSNeo Classic Space. A fan building style heavily based on the 'Classic' period of Space sets, which LEGO® produced from 1979 to 1987. Learn more at Neo Classic Space.
Parts or piecesParts are what I call LEGO® pieces/bricks. They are different to elements because each part can come in many colours and these differently coloured parts are called elements.
PolybagsThese are the small models that come in little plastic bags. They're often for promotional purposes and not released globally, which is a carrot on a stick to certain collectors!
POOPParts Out of Other Parts. A poor acronym but given it's a bit naughty, it's popular. It refers to those parts that cause strong emotions in AFOLs because they could be built from several smaller parts, which is taken as evidence of dumbing-down of the System. Usually referenced during discussions that begin, "when I were a lad..."
PrintsElements with printing on them.
RoriesAn AFOL nickname for 2X4 Bricks that is so friendly and natural it stuck immediately for me. It's possibly not widely used outside of the UK, given that it is quasi-Cockney rhyming slang. Back in the 1960s on east London street markets where LEGO construction was a popular way of filling in downtime for market traders, you could hear banter such as "pass us a two-by-foury guv, I'm making some apples today". The name soon mutated into 'rory' but never made the usual linguistic development of the rhyming word being dropped altogether in favour of another word in a rhyming phrase, although there were isolated incidents of the bricks being named 'Bremners' in the early 2000s. If you'd like to read more about this, you'll need to write your own porkies.
SNOT techniqueStuds Not On Top. (Those wacky AFOLs. Can't resist some humour based around bodily secretions.) Many elements have the little building studs on the sides of bricks. This enables 'sideways building' (as LEGO® prefer to call it) at 90° but there are many methods of building at 180° also. SNOT technique is perhaps to be considered the cornerstone of adult builders, allowing exciting new possibilities and finer detailing which LEGO would never include in an official set.
SystemToday the word System refers to groups of elements that are designed to connect together. There is more than one System; for example Technic elements are a separate System (even though many elements can also connect to the main System).
The word derives from the term System i Leg (System in Play, or System of Play); a concept developed by Godtfred Kirk Christiansen in the mid-'50s that transformed the LEGO® company. It focused their attention on the interlocking brick and how that could form the basis of an infinite range of compatible toy products. A great summary can be read at Brick Fetish.