An interview is a(n) in which one-on-one or small group question-and-answer sessions are conducted.

secondary source
unreliable source
serious source
primary source

An interview is a(n) primary source in which one-on-one or small group question-and-answer sessions are conducted. Because it comes from the person who actually has the knowledge on something. Primary sources are sources gathered first hand and interviewing is one of them. No matter how subjective it might be of how you would want to differentiate if it is fact or opinion, it is still a primary source.  

A fact is something – news, information, a talk, a seminar, etc., that is telling the truth and objective. This could be referenced by the people listening to it. An opinion is a declaration of the person’s thoughts and suggestions that is possibly subjective in nature. This cannot be referenced since it is declared by basing of emotions or one’s own perception on the information.