A spline is a long strip of wood (lath) that is fixed in a number of points. In older days splines were often used in shipbuilding to mark the curve of the hull. The lath will then take the shape which minimizes the energy required for bending it between the fixed points, and thus adopt the smoothest possible shape. Later splines have been made from rubber, steel, and other elastomeric materials.

Spline devices are used for bending the wood for pianos, violins, violas, etc. The Wright brothers used one to shape their wings.

In 1946 mathematicians started studying the spline shape, and derived the piecewise polynomial formula known as the spline curve or function. This has led to the widespread use of such functions in computer-aided design, especially in the surface designs of vehicles.

A spline also denotes a series of serrations or other shapes on a shaft to prevent rotation of a mating piece. For instance, a gear might be mounted on a shaft using a male spline on the shaft that matches the female spline on the gear. Splines are typically cut with a broach.