confused with << EOF EOF

Shell Programming and Scripting
1

Hi friends ,
I am confused with << EOF
EOF
Most of the cases I found

sqlplus $db_conn_str << EOF
some sql staments
EOF

another exapmle is

 
#!/bin/sh
echo -n 'what is the value? '
read value
sed  's/XXX/'$value'/' <<EOF
The value is XXX
EOF

so I want to know what is it .

2

'man ksh' and searching for 'here-doc' yields the following:

     << [-]word
           The shell input is read up to a line that is the  same
           as word, or to an EOF. No parameter substitution, com-
           mand substitution, or file  name  generation  is  per-
           formed  on  word.  The  resulting  document,  called a
           here-document, becomes  the  standard  input.  If  any
           character  of  word  is  quoted,  no interpretation is
           placed upon the characters of the document. Otherwise,
           parameter  and command substitution occur, \NEWLINE is
           ignored, and \ must be used to quote the characters \,
           $,  `,  and  the  first  character  of  word.  If - is
           appended to <<, then all  leading  tabs  are  stripped
           from word and from the document.