They wave when someone says 'bye-bye';

有人说“bye-bye”时，他们会摆摆手；

youdao

Mommy's going to work. Wave bye-bye.

妈妈要上班了。宝贝，来挥挥手说再见。

youdao

So wave bye-bye to everything you knew and set out as you would for a good holiday.

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So count me among those people who would love to wave buh-bye to anti-virus software.

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As he begins to play, I wave good-bye, and he responds with a suspicious glance in my general direction.

NPR: The Redemptive Power of Music, and Friendship