What do single-ended and differential mean?

Single-ended and differential refer to the reference for a voltage. For a single-ended measurement, the LabJack converts the difference between the voltage at an input and ground. For a differential measurement, the LabJack converts the difference between the voltage at one input and the voltage at another input that is not necessarily ground. On the LabJack U12, analog inputs can set as single-ended or differential via software. Analog inputs on the LabJack UE9 are single-ended only, so an instrumentation amp is needed to convert a differential signal to single-ended, or a pseudo-differential measurement can be made by taking the difference of two single-ended measurements.