In physics, especially in fluid mechanics, flow is quantified as "flux", which is the rate at which something flows through a given cross section (vis. a surface). See also rate of fluid flow.
Flow, in psychology, is the feeling of complete and energized focus in an activity, with a high level of enjoyment and fulfillment as described by Mihaly Csikszentmihalyi.
Flow in television is a term used about how channels try to hold their audience by announcing the coming programs.