WordNet (r) 3.0 (2006):

real-time
    adj 1: of or relating to computer systems that update
           information at the same rate they receive information

The Free On-line Dictionary of Computing (30 December 2018):

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)