There are many principles used in application programming. The interviewer is asking you about one of these. You should be able to easily answer this question based on your education and experience. The key is to use non-technical, easy-to-understand language when describing a principle to the interviewer. You may not be familiar with the depth of their technical background or their ability to understand complex concepts. Communicating clearly and effectively helps you in the interview and demonstrates your ability to collaborate with individuals from across the organization regardless of their technical knowledge. Interviewers are always looking for this skill when interviewing solutions architects.