splines

noun

1. Long thin piece of metal or wood.
2. A rectangular piece that fits grooves like key seats in a hub and a shaft, so that while the one may slide endwise on the other, both must revolve together.
3. A flexible strip of metal or other material, that may be bent into a curve and used in a similar manner to a ruler to draw smooth curves between points.
4. Any of a number of smooth curves used to join points.