IPA: /ˌɛkstrəˈkɜːrɪkjʊlər/
KK: /ˌɛkstrəˈkɜrɪkjələr/
Related to activities that are not part of the regular school curriculum, often organized and approved by the school, such as sports or clubs.
She participates in several extracurricular activities, including the debate team and the soccer club.
Extracurricular is formed from "extra-" (meaning outside) and "curriculum" (from Latin "curriculum", meaning a course or a running). The word refers to activities that are outside the regular course of study.
Think of activities that are 'outside' ('extra-') the regular 'course' ('curriculum') of school — that's what extracurricular means.