Real-timeAn operation is called a Real-time operation if it occures before the system to be controlled gets unstable. A Real-time operation must not necessarely be very fast. Slow systems can allow slow Real-time operations. This applies for every dynamically changing system, no mather of what kind it is.
A typical example could be to break a car. If the driver can stop the car before it hits the wall the operation was in Real-time. If the car hits the wall it was not. Many machines require Real-time controller to avoid that they get unstable, that means destroy them-selfs, injure people or demage other objects.
At this point we can add that an operation is Real-time if the summation of reaction-time and operation-time is shorter than the maximum allowed delay. For the example of a banking-system this would mean, that if anaccount-owner receives a payment, the time required by the human operator to get to know about the transaction and book it should be faster, than the account-owner starts worrying about his money.