Three angle brackets,<<< What do you mean?

Three angle brackets What do you mean,,<<<?
Title, the <<<admin_option and admin_option below.
<<<entry_display and Entry_display
Look at the feeling of a little comment, and do not feel like a comment, please which can explain it? Thank you. Feel a little bit to ensure the meaning of HTML structure. Thank you
$entry _display. = <<<admin_option

<p class= "Admin_link" ><a href= "{$_server[' php_self ']}?admin=1" >add a New entry</a></p>admin _option;///////////////////////////////$entry _display. = <<<entry_display<p class= "POST" >
 
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The meaning of the code snippet!
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PHP Code
 
 
  
$somevar = <<<someword     put your code or words Heresomeword;
 

 
 
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