The term “shiplap” comes from the days when ships were handmade. Wooden planks would be attached to the ship’s frame with adhesive but because wood expands and contracts over time based on temperature and weather, the boards would separate, causing leaks.
Finally someone realized that if the planks on one tier overlapped the planks just below them, the adhesive would have more contact area and the planks would hold better than when the planks abutted each other. This style became known as “shiplap” and today is sometimes used purely for design purposes, such as with our panels. You often see this Shiplap style on the sides of houses.