Supplementary lessons or remedial classes given to make up for regular instruction, often for students who need extra help or exam preparation.
数学が苦手なので、放課後に補習を受けている。
I'm weak at math, so I take supplementary lessons after school.
夏休みに補習があり、毎日学校に来なければならなかった。
There were remedial classes during summer vacation, and I had to come to school every day.
試験前に希望者だけの補習が行われる予定だ。
There will be optional supplementary lessons before the exam for those who want them.