An extracurricular activity is any activity that is not directly related to your course work. For example, if you tutor, if you are a teaching assistant, if you do research, if you play on a sports team, if you volunteer, if you shadow, those are all extracurricular activities. They are very important at most schools, because the school wants to see that you are a well-rounded applicant. They want to know that you have more to offer than just academic excellence or great test scores. Also, extracurriculars can set you apart from other applicants. I hope this was helpful, if not let me know and I'll try to explain it differently 🙂