自习 zìxí to study outside of class time

to study outside of class time (reviewing one's lessons); to study in one's free time; individual study

How to remember 自习: 自 self + 习 practice = to study outside of class time.

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School-specific term for studying on one's own during a scheduled but unsupervised period, often as the noun 自习课 (zìxíkè, study hall).
去自习 (qù zìxí) - to go do self-study, a very common thing for Chinese students to say about library or classroom time.
Different from 自学 (zìxué), which means teaching yourself a subject with no formal class involved at all - 自习 still happens within a school's schedule.
Common in student life; rarely used for adults studying independently outside school.