Activities that are done outside of usual school work like hobbies, sports and personal development are known as extra-curricular activities. Super curricular activity is additional subject learning that goes beyond what was covered in class. Both of these can help you stand out in your college or university application.
These resources will give your lots of ideas of how you can boost your opportunities through extra activities.
A useful selection of suggested reading lists and resources which has been gathered from Cambridge departmental and college websites, other univesrities and various other online sources.