A passthrou device is used in conjunction with a computer to reprogram vehicle control modules through the OBD-II/CANbus port. Each manufacturer has their own type, but SAE International standardized the J-2534 universal requirements in 2004, requiring all manufacturers to allow vehicles sold in the United States of America and Europe to accept powertrain reprogramming through specific universal parameters.
References
Pass through device (automotive) Wikipedia(Text) CC BY-SA