A system is responsive if it gives results in a reliable manner. If you talk to me, I will answer your question or, at least, tell you that I do not know the answer or that I was not able to understand the question. Yes, it would be better to get the answer, but if a system cannot give that to you, it is still expected to give something back. If you have past experience with client-operating systems from just ten years ago, and some old computers, you can understand this. Getting a rotating hourglass is frustrating. You just do not know whether the system is working to get you the answer or whether it is totally frozen.
A reactive system has to be responsive. The response should come in a timely manner. The actual timing depends ...
