Technically, it' s not really

What you are describing is Flex. Spine is actually a characteristic imparted via the manufacturing process that runs the length of the shaft, where it is most resistant to flex. Think of it as a kind of back bone.

Arrow makers always say spine, but what they are really talking about is flex. Can flex be affected by spine? Absolutely. Are spine and flex the same? No.

I think the intermingling of these two distinct terms is what is causing the confusion in the two threads going on about spine now...