Every active participant in a conversation is an interlocutor.
Example
In some oral exams, there is an interlocutor, who talks with the candidates, and an assessor, who marks them.
In the classroom
Successful communication in another language is being aware of your impact on the other interlocutor, especially if they are from another culture with different conventions. Some teachers spend time with learners looking at areas such as body language, facial expression and physical distance between speakers, all of which can have significant impact.
Further links:
https://www.teachingenglish.org.uk/article/three-activities-speaking-tests
https://www.teachingenglish.org.uk/article/listening-body-language