Source : Free On-Line Dictionary of Computing

real-time
     
        1. Describes an application which requires a program to
        respond to stimuli within some small upper limit of response
        time (typically milli- or microseconds).  Process control at a
        chemical plant is the classic example.  Such applications
        often require special operating systems (because everything
        else must take a back seat to response time) and speed-tuned
        hardware.
     
        2. In jargon, refers to doing something while people are
        watching or waiting.  "I asked her how to find the calling
        procedure's program counter on the stack and she came up with
        an algorithm in real time."
     
        Used to describe a system that must guarantee a response to an
        external event within a given time.
     
        (1997-11-23)