WordNet (r) 3.0 (2006):

real time
    n 1: the actual time that it takes a process to occur;
         "information is updated in real time"
    2: (computer science) the time it takes for a process under
       computer control to occur

The Jargon File (version 4.4.7, 29 Dec 2003):

real time


    1. [techspeak] adj. 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 canonical example. Such applications often require special operating
    systems (because everything else must take a back seat to response time)
    and speed-tuned hardware.

    2. adv. 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.?