指的是用一块石头砸中两只鸟。

It means to hit two birds with one rock.

现在用来表示一个举动，达到两种目的。

Now used to mean one action that serves two purposes.
 

• Tā jì xuéxí le hànyǔ, yòu jiāo dào le péngyou, zhēn shì yī shí 'èr niǎo.
• 他既学习了汉语，又交到了朋友，真是一石二鸟。
• He not only learned Chinese, but also made friends, hitting two birds with one stone.