Accessory: An object intended to be clipped into a minifigure's hand. Example: This movie director's clapboard and megaphone.
Baseplate: Even thinner than a plate, and generally larger, baseplates provide a good building surface. They are coated with building studs, so you can place bricks and plates right on top of them. Although they come in various sizes, smaller 'standard size' baseplates are 10 inches square and are green or blue. Larger baseplates are 15 inches square and are gray.
Brick: The standard LEGO piece. Each is 3/8 of an inch high. (.94 cm) Bricks are usually square or retangular. The 'classic' LEGO piece is a 2x4 brick.
Group: A group of related sets/models. For example, several spaceport models make up my Lego City Space Administration group.
Minifigure: A LEGO person. Standard minifigures are 1.5 inches high. (3.75 cm) This leads me to an interesting calculation. Scaling up 1.5 inches to a fairly normal height for a human, 6 feet, most of the LEGO world is on a 1/48th scale. (1/50th if you want an easy number)
'L' Brick, 'L' Plate: An exception to the rule that bricks and plates are square or rectangular. 'L's have three studs angled at 90 degrees.
Piece: A brick, plate or special piece.
Plate: A LEGO piece that is 1/3 the height of a brick, 1/8 of an inch high. (.31 cm) Plates are almost always square or rectangular with a couple of exceptions.
Round: Another exception to the rule that plates and bricks are square or rectangular.A round brick or plate. Round bricks come in diameters of 1, 2 and 4 studs. Round plates come in diameters of 1 and 2 studs. 1-stud diameter round plates are often transparent.
Set: One thing built out of LEGOs, or a very small group of related things. Also 'model'.
Slanted Piece: A brick that has a slant to it and only one row of studs at the end. Most slanted bricks are 2x2, 1x2, 1x3, 1x4, 2x4 or 4x2 at the base.
Special Piece: A LEGO that is neither a brick nor a plate. There are hundreds of different special pieces. This one is called a 'Radar Dish'. (It's not really rainbow colored, it just appears that way because it's transparent, and I photographed it on a rainbow-ish background.)
