This interview question can come in many flavors: What do you want to do with your life? What are your goals? What is your dream job? What do you want to do with your college degree?
Realize that you definitely do not need to know what you want to be doing ten years from now. College is a time of exploration and discovery. Many prospective college students have not yet been introduced to the fields that will define their future careers. The majority of students will change majors before they graduate. Many students will have careers that aren't directly connected to their undergraduate majors.
But the college admissions folks do want to see that you have thought about the future, and they'd like to know how college fits into your vision of your future. For advice on how to approach a question about your future plans, check out these college interview tips.