Grain Direction (long grain, short grain)

Machine made paper is made up of fibers which tend to line up in one direction due to the nature of the manufacturing process.

This produces a preferred direction, or "grain," along which it is easier to fold, bend, or tear the paper.

Cut sheet laser printers or copiers for example generally use long grain paper in which the grain runs parallel to the long side of the paper.

You will see paper marketd as 12x18 or 18x12 depending upon which direction the grain runs.