regular curriculum; required subject
Refers to subjects or courses that are part of the official, prescribed curriculum, as opposed to extracurricular or optional activities.
At this school, club activities are also popular in addition to the regular curriculum.
正課として英語と数学が必修です。
English and mathematics are required as part of the regular curriculum.
正課 refers to the regular required curriculum, the opposite of 課外, which means activities outside that curriculum.
Compound of 正 (correct, formal) and 課 (lesson, section), referring to formal or prescribed coursework.