According to ODLIS, the reference interview is "the interpersonal communication that occurs between a reference librarian and a library user to determine the person's specific information need(s), which may turn out to be different from the reference question as initially posed...A reference interview may occur in person, by telephone, or electronically (usually via e-mail) at the request of the user, but a well-trained reference librarian will sometimes initiate communication if a hesitant user appears to need assistance".
Approachability, interest, listening/inquiring, searching, and follow up are five steps to conducting a successful reference interview based on American Library Association(ALA). Basically with following these steps, we're trying to figure out the patron information needs and helping them find it.