Different dictionaries describe it in various ways, so I will take another liberty here, and give you the synopsis that I often use in the magazine: "Pith is: the soft core of various things bones, feathers, etc.;
(I; give; you; the synopsis that I often use in the magazine) (the synopsis; use; L:in the magazine; T:often) (Pith; is; the soft core of various things)
I the synopsis Pith
give use is
you the synopsis that I often use in the magazine
L:in the magazine T:often
the soft core of various things