Real time software is what people are more used to. When input is entered a response comes back immediately. (Note - Immediately in computer science terms normally means less than a few seconds). This is important for more mission critical systems, such as nuclear power plant control systems or air traffic control. If you had to wait for a few minuets if the reactor was overheating it may explode. As such the software must respond immediately.

Transactional based systems are also considered to be real time. Consider travel agents with multiple stores across the country. If one store books the last seat of a cut price holiday it should no longer allow any other store to book. The transaction needs to happen fast enough to stop multiple bookings from occurring.

Note - For the course the idea of a travel agent booking tickets is considered as a real time system. However this is not true. Anything which goes over a network can only be a real time system if there is a specific bounded upper latency. What we mean by this is that there is a maximum amount of time a packet of data will take to travel over the network. Anything involving the internet will not have such an upper bound (or the upper bound will be too large). This is because there is no way to predict what route a packet will take when going over the internet. Booking systems use concurrency and transaction management rather than relying on the upper bound on the network. Technically the above example is wrong.