This is another question looking towards job commitment. Some people go through jobs like socks because they don't have a life plan, and your answer can show insight into this. It can also be used for finding out if you are the type that sets goals at all in life, because those that make long-term goals are usually more reliable. Also, your goals can provide insight on your personality too.

You should respond with an answer that shows progression in your career is on track with your route in the company. It's important to do your research on company prospects, this way you understand what to expect and if it's in your long-term goal. Interviewers don't want to set you on a path that won't provide the results you want, resulting in you resigning.