撞肘是一种非正式的问候方式，两个人通过肘部轻触或者撞击来问候对方。

The elbow bump is an informal greeting where two people touch, or tap, elbows.

youdao

在英语中有很多问候的方式可以用在正式和非正式的场合里。

There are lots of ways of greeting in English which can be used in both formal and informal situations, eg: How are you doing?

youdao

现在“ciao”是用于非正式场合的问候语，但它的本意“仆人“，可追溯到古时“我是你的仆人”这一用法，与“我是你卑微的仆人”在书信署名里传达的敬意一致。

Now the word “ciao” is casual, but its meaning “slave, ” harkens back to “I am your slave, ” the same sense of respect a person signing off with “your humble servant” tried to convey.

youdao