what's the detail meaning of 'Common symbol'?

Question

In nm (binutils cmd) manual:

"C"        The symbol is common.  Common symbols are uninitialized data.
           When linking, multiple common symbols may appear with the same
           name.  If the symbol is defined anywhere, the common symbols
           are treated as undefined references.

What's the meaning? Can somebody explains the sentence.

Answer 1

说明这个标示符是通用的.通用标示符是没有初始化数据的.当我们在使用标示符的时候,多个标示符也许会显示一样的名字,并且可能在任何地方使用到这样的标示符,这时候我们就可以利用通用标示符了.

FYI,hope this can help you any more.