Server is a String property that contains information about the software used by the server to handle the HTTP request. Server can contain multiple product tokens and comments identifying the server and any significant subproducts. 

For example: 

  Server: CERN/3.0 libwww/2.17

Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks against software that is known to contain security holes. Server implementors are encouraged to make this field a configurable option.