I often see these terms used wrong, so here's a simple reminder to how they should be used.
Spine= Backbone (enough said)
Spline= thin strip of wood, metal of vinyl

So graphite rods have a "spine" (or backbone) the correct use of the term also tells you which side the guides go on!

A bamboo rod is made from "splines", long thin strips of wood(reed actually).
I hope this helps!

[This message has been edited by Ray (edited 10 June 2006).]