Some examples of Google search:
风中的树_新浪博客
历史转折中的邓小平_电视剧_央视网
What is the meaning?
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Sign up to join this communitySome examples of Google search:
风中的树_新浪博客
历史转折中的邓小平_电视剧_央视网
What is the meaning?
I guess it becomes popular on Internet due to web technology favor. Most of web servers are built on Unix(or similar, like Linux) OS. Underscore is widely used as space replacement since space it's not allowed for variable name in most of the programming languages. Also, web pages usually in a hierarchical structure, and web page title usually contains the hierarchical information for SEO purpose. Thus the underscore symbol is introduced into web pages as a separator, although some programmers may choose the minus symbol instead of underscore.
As a conclusion, the underscore is nothing with Chinese, but a web stuff.
The underscore is not used before the Internet came to China. Since your two examples are all web page titles, I guess that the underscore just functions as a separator.
Underscore in Chinese is written under the word you're writing. It means that the word above the underscore is a noun. (Usually a name, or a place)