Step 1: Anchor the definition in its purpose:
An interview is essentially a purposeful conversation designed to systematically collect information relevant to a research question, distinguishing it from casual conversation.
Step 2: Organise types along a flexibility spectrum:
At one end sits the fully structured interview (rigid, standardised, good for large-scale surveys); at the other sits the unstructured interview (flexible, exploratory, good for in-depth case studies); the semi-structured interview sits between the two, balancing standardisation with flexibility.
Final Answer:
Interview method = a systematic, purposeful conversation for data collection; its main types along the structure spectrum are structured, semi-structured and unstructured, plus mode-based types like personal, telephonic and group interviews.