Binding Energy Notation

I was reading a paper today with a section on sodium, magnesium, and silicon isotopes. I came across a part that read "two-neutron binding energies S_2n" and thought this was a slight topic change to the two-neutron binding energy of sulfur. After all, sulfur is really close to the aforementioned elements in the periodic table. Another interpretation then occurred to me--"S" apparently stands for binding energy. This was, to me, a little unexpected, since just as there's no "I" in "team," there's no "S" in "energy" (admittedly, there's no "S" in "entropy," either). Where did this notation come from? Edited to add: Oh, "S" for "separation energy," a synonym. I can cope with that notation.
 
Incidentally, while endeavoring to ascertain the origin of this notation (such process consisting mainly of Googling the term), I came across the Wikipedia article on binding energy, which is very informative and heavily nuclear-oriented. I especially like the two-sentence explanation of why both nuclear fusion and nuclear fission produce energy.