This is your chance to sell yourself. Before any interview you should make a list of your "Unique Selling Points" - anything which makes you a strong applicant: good academic results, relevant work experience, evidence of leadership or other relevant skills for the job. You need to back up these points with relavant examples of where you have demonstrated these. This question may be phrased in different ways such as "How would your best friend describe you?", "Why should we take you rather than the other applicants?" or "Tell me something about yourself". Whichever way it is phrased, this is a golden opportunity to convince the selector that you are the right persion for the job: don't waste it!