questions

As the title says, what is the "Economy" part of the table?

something with how much damage it does and how many stat points are needed. Though i dont know how Ender calculated it (i would do: total damage/ (reqstr + reqdex) ), higher is better. Meaning you're getting more damage for your stat points.

ah right. Ender does the same, but with added str and dex.
So the formula is: Economy = total-damage / (add-str + add-dex)

Just to add on what Mainor said, a weapon with higher economy is better on paper, as you invest fewer stat points for each point of damage gained. This is only a general rule, as many of the weapons with the best economy are pure dex weapons, which still get destroyed by most other builds :/

I just pulled up the code and here's what it seems to be:

economy = (min_dmg + max_dmg) / ((req_str - 10) + (req_dex - 10))

If req_str or req_dex is 0, then 0 is used instead of "req_xxx - 10".