Bad
Substandard, Delinquent
noun, な adjective, の adjective
Something that's not good is bad or substandard. This usage is more formal and frequently paired with other kanji compounds. Alternatively, it can refer to someone who is a delinquent, in which case it is often used as a standalone word.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
ビエト、今日はちょっと不良な感じのヘアスタイルだね。
Viet's hair style today kind of looks like a delinquent's, don't you think?
不良パーツが見つかりました。
Malfunctioning parts were found.
あの不良少女は、急に成績が大幅に下がった後、ギャングの一員になったんです。
That delinquent girl’s grades suddenly dropped drastically and then she joined a gang.