It contains information on headers, paths, and script locations.
Here is a listing.
$_SERVER['PHP_SELF']= Filename of the currently executing script
$_SERVER['GATEWAY_INTERFACE'] Version of Common Gateway Interface (CGI) being used
$_SERVER['SERVER_ADDR'] IP address of the host server
$_SERVER['SERVER_NAME'] Name of the host server.
$_SERVER['SERVER_SOFTWARE'] Server identification string. Maybe Apache x.y
$_SERVER['SERVER_PROTOCOL'] Name and version of protocol HTTP/1.1
$_SERVER['REQUEST_METHOD'] Request method Get or Post.
$_SERVER['REQUEST_TIME'] Timestamp of the start of the request.
$_SERVER['QUERY_STRING'] Query string.
$_SERVER['HTTP_ACCEPT'] Accept header from the current request
The Accept request-header field can be used to specify certain media types which are acceptable for the response. Accept headers can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request for an in-line image.
More details here
$_SERVER['HTTP_ACCEPT_CHARSET'] Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
The Accept-Charset request HTTP header advertises which character set the client is able to understand. Using content negotiation, the server then selects one of the proposals, uses it and informs the client of its choice within the Content-Type response header
More information here.
The Accept-Charset request HTTP header advertises which character set the client is able to understand. Using content negotiation, the server then selects one of the proposals, uses it and informs the client of its choice within the Content-Type response header. Browsers usually don't set this header as the default value for each content type is usually correct and transmitting it would allow easier fingerprinting.
$_SERVER['HTTP_HOST'] Returns the Host header from the current request
$_SERVER['HTTP_REFERER'] Returns the complete URL of the page from which the current page was called
$_SERVER['HTTPS'] Is the script queried through a secure HTTP protocol
$_SERVER['REMOTE_ADDR'] IP address from where the user viewing the page
$_SERVER['REMOTE_HOST'] Host name from where the user is viewing the current page
$_SERVER['REMOTE_PORT'] Port being used on the user's machine to communicate with the web server
$_SERVER['SCRIPT_FILENAME'] Absolute pathname of the currently executing script
$_SERVER['SERVER_ADMIN'] Returns the value given to the SERVER_ADMIN directive in the web server configuration file.
$_SERVER['SERVER_PORT'] Port on the server machine being used by the web server for communication (such as 80)
$_SERVER['SERVER_SIGNATURE'] Server version and virtual host name which are added to server-generated pages
$_SERVER['PATH_TRANSLATED'] File system based path to the current script
$_SERVER['SCRIPT_NAME'] Path of the current script
$_SERVER['SCRIPT_URI'] URI of the current page
Use the following code to print a complete list of keys and values in $_SERVER.