[Halon]

Understanding open loop vs. closed loop generically is pretty simple. It simply is referring to the ECU feedback loop (feedback being the O2 signal) either being open or closed.

Open Loop = No O2 feedback, the feedback loop is open/broken/not-in-use.
Closed Loop = O2 feedback, the feedback loop is now closed/in-use.

Stock narrowbands are calibrated to read stoich (14.7). So closed loop operation would be scenarios where you expect to be at 14.7. This would be idle, cruising, low load scenarios.

Open Loop would be when you don't want to be at 14.7, so you just hard set your tables to put you at say 11.5. So open loop would be scenarios you don't want to be at 14.7 and you want to be at something else. So WOT, heavy throttle, high load, cold start/warm up kind of scenarios. Times when you're running at 11.5 and the O2 is feeding back to the ECU saying "Hey your not stoich", the ECU says I don't care I don't want to be stoich right now so I'm ignoring your feedback.

Open and closed both use fuel tables. Closed loop just has the added benefit of O2 feedback so if for some reason your table doesn't put you right at that perfect stoich mixture, the ECU can detect that it's not stoich and can compensate based on that feedback.