An unstructured interview may also be known as an informal interview. Instead of the hiring manager deciding on the interview questions in advance, they ask what they want to at the time. This gives more freedom for the interview to change in direction and the interviewer can probe more into the areas that are raised during the interview.
These interviews are more commonly used in a first round of interviewing that precedes structured interviews with a smaller number of candidates. This offers the opportunity for the interview to find out more about certain areas of a candidate’s experience or skills that were missing from the CV and cover letter.