I think that intercativity is everywhere around us. Interactivity is a communication. Communication for us is our friends, family, other people with whom we meet at any time of our life. Technical communication: Internet, cells, videos, etc.
Naturally, interactivity is not only between people. It can refer to software, where exists data or commands. Interactive software includes most popular programs, such as word processors or spreadsheet applications.
One more example of interactivity is a Virtual Reality. This program is a technical fantasy, which hepls people to interact with computer-stimulated environment, as a real or imagined dream.