A Brick is a general term for any LEGO part. However, technically it is an element three plates or more thick, rectangular in shape, with at least one stud on top. LEGO studs are tiny round dots on a brick that can peg into other bricks to make them stack or connect. The bricks often have stickers or printings on them, like many other LEGO elements. They come in many sizes, from a tiny 1x1 brick to the largest 12 x 24 brick plates. The original brick did not have the "Sockets" that the present-day brick had. They were just a tub on the inside. This made it hard to stack them and LEGO corp realized people were getting angry about that and added the sockets.
Bricks are referred to by their dimensions. When they are only three plates high, they can be referred to as a 2x2 brick. If they are taller, then a third number is added, referring to their height. An example is a 1x2x5 brick, which is a relatively rare brick only used in certain sets.
The only odd-number bricks are the 1x and 3x sizes. All sizes above are even numbers.
The height of a LEGO brick is around 9.6 millimeters. The length and width of a 1x1 LEGO brick are 8 millimeters, which means that for every additional part of a brick (e.g. 2x1), every part adds up 8 more millimeters, which means that the width is 16 millimeters and the length is 8 millimeters.
Known in other circles as beams, these bricks have hollow studs and have holes through them for pins. The holes have a diameter of 4.8 mm.