DA and AD are terms we often hear when using PLC.
D refers to the digital quantity, that is, Digital, and A refers to the analog quantity, that is, Analog.
Digital information is discontinuous, while analog information is continuous.

Common digital signal types include PNP, NPN, relay, counter, pulse and so on.
Common analog signal types include current, voltage, thermocouple temperature, thermal resistance temperature, pressure, etc.
DA is digital to analog, AD is analog to digital.
Since the analog quantity can be collected, the PLC output command must be a digital quantity, so DA usually refers to the input type IO, and AD refers to the output type IO.