What is spine?

[upsguy]

Is it the weight of the arrow or the stiffness of the arrow? If it is stiffness, then how is it measured.

Another question, if an arrow says its weight is 10 gr. per inch, then a 28" arrow would weigh 280 grains, but that doesn't include the weight of vane, nock, and insert, does it?

[pdq 5oh]

Spine refers to the stiffness of the shaft. A 1.94 lb weight is suspended from a shaft on 28" centers. The amount it deflects (bends) is measured. The deflection is the spine of the arrow. An arrow that deflects .400" would have a spine of 400. Some companies use numbers that descend to designate spine. A 500 would be weaker than a 300. Others use an ascending scale. A 300 being weaker than a 500.
Grains per inch is raw shaft. Total arrow weight would be a finished arrow. Vanes, nock, insert, and point are all added to shaft weight, for total weight.