1. Allowing or relating to continuous two-way transfer of information between a user and the central point of a communication system.
2. Immediate two-way communication between a source of information and a user, who can initiate or respond to queries.
Input/Output or i/o
Communication between an information processing system (such as a computer) and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it.