The NHS is a large organisation that has thrived over the years and has grown to be one of the largest employers in the world. Consider what makes them successful in the healthcare industry, what sets them apart, and how you can contribute to their short and long-term successes. The interviewer is able to learn a lot from your response, including how you define success, what types of goals you set, and how you measure success. Speak about how you define success professionally and give examples that relate to the position you're applying for.