Interaction must be something that can interact. There are many ways to define interact. But to make it short, it is simply a process to communication. In order to form some kind of linkage or collaboration, we need to get in touch with 2 or more things in order to make it happen. And this process is interaction. In a modern setting, interaction could be a user-consumer relation, or a person-person, person-object relation. But to me, interaction is a two way give and receive, and end up with a change in both side that is forming the interaction. For example, when we are scrolling down a website on our phone or computer, the information on the device changes, and we simultaneously receive new information in the process.