Structured interviews follow a predetermined format. Before inviting candidates to interview, the interview panel or hiring manger to decide on the set of questions to ask each candidate. Then each person they interview is asked that exact same set of questions. This allows the interviewers to score candidates on their answers and compare candidates more easily.
Anther common term for a structured interview is a standardized interview. These types of interviews are often used in research to gain data as well. These interviews may contain both behavioral and situational interview questions. At the end, the interviewer will often ask the candidate if they have any questions as well.