Oxygen Sensor, Engine Tuning Fundamentals

What exactly is closed loop tuning? ive come across that term quite a bit while researching about tuning the 2azfe.

Closed Loop refers to the ECU using an oxygen sensor to provide feedback on the mixture and the ECU will adjust the fuel to match a target (Lambda, Equivalence or AFR -- different versions of the same thing). The current amount of fuel change is often referred to as the Short Term Trim, and over time and ECU may build up a value known as a Long Term Trim (if the engine is constantly lean, the long term trim will start by adding fuel).

On some platforms, you tune by adjusting the fuel table until the Short Term Fuel Trim (STFT). The nice thing about this is generally the STFT if in percent represents exactly how much you need to change a particular cell in the fuel table.