1. Something put into a system or expended in its operation to achieve output or a result, especially: a. Energy, work, or power used to drive a machine. b. Current, electromotive force, or power supplied to an electric circuit, network, or device. c. Information put into a communications system for transmission or into a computer system for processing. d. Any of the items, including materials, equipment, and funds, required for production. 2. a. The act of putting in; infusion: a steady input of fuel. b. An amount put in. 3. Contribution of information or a comment or viewpoint: a discussion with input from all members of the group.