Unstructured interview
An unstructured interview has no fixed question set or scoring criteria — the interviewer improvises based on the CV and the flow of conversation. It is the most common format in practice and among the weakest predictors of job performance.
Unstructured interviews feel effective, which is why they persist. Interviewers consistently report high confidence in judgements formed this way. That confidence is not matched by outcomes.
The failure mode is that the interview measures how comfortable the conversation was rather than whether the candidate can do the job — which systematically favours candidates similar to the interviewer.