Volunteer experience is all unpaid activities and committees you have been involved in. The interviewers ask this question to gain insight into your personality traits and hobbies that are important to you, such as being on a leadership council or debate committee. Volunteerism also shows the interviewers that you like to give back to the community and are selfless with your time. Tell the interviewers about your volunteer experience, no matter how small it may seem. The more volunteer experience you have, the better your chance to match with the program.