I will use the term "interview" to cover a wide range of research activities from the most "informal", "open-ended" interviews to the use of "formal" instruments in survey research. In order to be considered an interview according to my definition, the collection of data must occur in a face-to-face situation. The interaction must also occur in a research context and involve the posing of questions by the investigator.
Briggs, Charles L. Learning How to Ask: A Sociolinguistic Appraisal of the Role of the Interview in Social Science Research. Cambridge University Press: Cambridge, 1986. p.6-7