"Checked and Unchecked". I think I failed this question because I gave an explanation of the two types, but it was an awkward fishing expedition as he said I was correct, but what where the names of these types? I had to google it after the interview - my explanation was spot on, I had forgotten these names. If you get asked this question, just say "Checked and Unchecked", I doubt the interviewer is going to press on for more detail.