Interaction is not giving a short, one-sentence answer to this question. In some ways, what goes on in a worst-case EFL conversation class is a series of monologues. Because they are contaminating the Earth. And this does not happen a lot because the teacher is constantly contributing, egging on and prodding the L2s into participating. They, instead, look towards the teacher for guidance and, perhaps, permission to talk.
Interaction is, once again, when the whole class is engaged in a group conversation.
Interaction can involve the teacher but it must involve the L2s. Next, the headings should be explained to the L2s. I agree entirely. I don't know. I am not sure.