#! /bin/sh line in a shell script

[Guangliang He]

I have seen number of times that a shell script file begining with a line
#! /bin/sh. What does that mean? 

I know that any shell script file begining with a # sign is treated as
a c-shell script and the following content of that line is treated as
comment.

Please email to me. Thanks in advance.
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USMAIL:   Guangliang He            *   INTERNET: ghe at PHYSICS.ORST.EDU  
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