I assume that you are asking how you should respond to a question like this on an application for admission to a particular university. If so, your best bet is to answer honestly, but also to try your best to find at least some academic or cultural aspects of the university that could plausibly have led you to apply.
For many people, the decision to apply to a given university is as much about convenience and social factors as anything. They apply to a given college because it is near to their home. They apply to it because people they have known from previous high school classes have gone there. The problem with this is that it does not make for a very impressive application. It does not make the admissions officers think that you really want to go to their school for any positive reason.
Therefore, it is important to try to talk about the academics or the culture of the university. For example, if you are from a rural area and want to go to an urban college, you can talk about wanting to broaden your horizons and make yourself into a more well-rounded person. Or, if you are from a rural area and want to go to your local state school, you can talk about the importance of small-town life and values and how you want to go somewhere where you can have those things. Ideally, you would also be able to say something about the quality of the school’s program in whatever it is you want to study. However, this will be harder to say for most people because most people study things that are available at essentially any college.
Overall, then, I would say that you want to do anything you can to avoid simply saying that you applied some place because all your friends did. Try to identify reasons that make it sound like you have given some thought to the process of deciding where you want to go to college.