The lay describes the direction in which direction the wires of a strand or the strands of a rope are twisted around a central wire or core.
In a strand, if the wires are laid helically over a center wire in a left direction, the lay is called S-lay or left-lay
If the wires of a strand are laid helically over a center wire in a right direction, the lay is called Z-lay or right-lay
In a rope, the lay describes both the direction in which the wires are twisted in the strands and the direction in which the strands are twisted in the rope. If the wires are twisted into the strands in a left hand direction and the strands are twisted into the rope in a right direction, this is described as sZ or right hand regular lay. If both wires in the strand and strands in the rope are twisted in a right hand direction this is described as zZ or right hand Lang lay.
Variations are zS (left hand, regular lay) and sS (left hand, Lang lay). If not specified otherwise, sZ (right hand, regular lay) will be supplied.