What it means
Is not, or "no" in reply to a 是 question.
When to use it
To soften a disagreement, add 也: 也不是 — "not really, either."
Examples
zhè这shì是nǐ你de的ma吗？——bú不shì是。
Is this yours? — No.
wǒ我bú不shì是lǎo老shī师。
I'm not a teacher.
tā他bú不shì是gù故yì意de的。
He didn't do it on purpose.
The full set of survival phrases for greetings, dining, shopping, and getting around, each with audio.