From WordNet (r) 3.0 (2006) [wn]:
real-time
adj 1: of or relating to computer systems that update
information at the same rate they receive information
From The Free On-line Dictionary of Computing (8 July 2008) [foldoc]:
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)