The definition of ambition or aim is a motivation or a strong urge to achieve something. If this question is asked in the UPSC interview, then you have already achieved a big goal that you have set for yourself.
You can answer like: "My ambition in life is to become a good officer who feel the pain of their citizen and try to solve their problems as much as possible. I want to take part in nation building through this great profession. I believe in the fact that everything is possible in the life with hard work and positive attitude, and I shall prove it true."
