It means, there are totally four inputs for ADC in which you can use these inputs as four single-ended inputs or two pseudo-differential inputs.
In single-ended mode, an analog signal that needs to be converted is converted with reference to the ground or reference voltage.
If the need arises to sense the signal ground or decouple the relative measurement result from the current carrying ground plane, you may need to
move to a pseudo differential input ADC. In this mode, a device is performing a differential measurement, but the differential that is sensed is a single-ended input signal measured with respect to the input signal ground level.