IO may refer to: An abbreviation I.O., a theater in Chicago, Illinois dedicated to improvisational comedy. Industrial organization, the field of economics that studies the strategic behavior of firms, the structure of markets and their interactions. Input/output, the collection of interfaces that different functional units of an information processing system use to communicate with each other. Image Orthicon tube, a TV camera used between 1946 and 1968. International Operations, a fiction… (More on Io)