The term "interactive" means "containing an element of interaction with the user , the viewer or the reader". The very word "interactive" consists of "inter" (between-) and "active" (effective).
Modern technologies allow you to make many things interactive, that is, in which the user can take a certain part. Interactive can be a computer display, an exhibition in a museum, a video, a school lesson, a theatrical performance or even a book. The ways to achieve interactivity can be completely different. So, if it's enough to include an element of a computer game in the video, in the case of a paper book the reader can be asked to go to a particular page, depending on his wish or answer to a question.