This is  universal sensor adapter V2.0, it can be accessed by digital input modules and analog input module. The module with Arduino sensor expansion board, in combination.Improvment compare with the old version,we add a 10K resistor between A & B, A & C respectively,so that you  needn't to connect a addition resistor while the sensor must have a pull-up or pull-down resistor. Why need a pull-up or pull down resistor, please refer to"Understanding pull-up and pull-down resistors"

 

Generally speaking, this terminal provides a much easier way to connect a switch or any modules that requires pull-up/down resistor to microcontroller .