The former is the former armed wing of Fatah, the latter of Hamas. Fatah is a (notoriously corrupt) secular nationalist organization. The story goes that Netanyahu tacitly supported and helped fund Hamas for many years as a check against Fatah consolidating power into a coherent Palestinian state.

The first is Fatah/PLO, who are in many ways much closer to, eg, the IRA (also nominally religiously inspired) than what we understand as modern Islamist terrorist groups.