What it means
じゃない is the plain negative form of the copula, meaning that a person or thing is not something. It follows nouns and na-adjectives and is common in casual speech and writing. It can describe the present situation or identity, while the polite counterpart uses ではありません.
Usage note
じゃない can also appear at the end of a sentence as a negative question or confirmation request, depending on intonation and context. Do not confuse this use with the straightforward negative statement shown here.
How to use it
これは学生ではありません。
This is not a student.
この町は静かではありません。
This town is not quiet.
これは学生じゃない。
This is not a student.
この町は静かじゃない。
This town is not quiet.
Example sentences
この建物は図書館じゃない。
This building is not a library.
あの人は駅員じゃない。
That person is not a station employee.
今日は休日じゃない。
Today is not a holiday.
この料理は辛いものじゃない。
This dish is not a spicy one.
その説明は正確じゃない。
That explanation is not accurate.