A brick is a fan term, usually derogatory, to describe a Transformers toy that has particularly low articulation. Most examples of bricks tend to be smaller toys that have been given limited articulation to keep costs down. The Throttlebots and the Duocons are prime examples. Some larger toys, however, can also be described as bricks, such as Powermaster Optimus Prime.
Due to the limitations of the toy technology of the time, bricks are usually molds originating in Generations 1 and 2; however, some more modern toys such as Armada Super Optimus Prime have earned the same description. When modern toys are bricks, it is usually because a gimmick of some sort makes it difficult to add more articulation.