var ใน php คืออะไรครับ var $abc = "varมันคืออะไรครับ"; มีประโยชน์ยังไง ใช้ยังไงคับ

<?php
class FirstClass{
	var $surround = 'Hello World!!';
	
	public function __construct(){
		echo $this->$surround;
	}

}
?>

<?php
require_once(WEB_LIB_DIR . 'AdminAction.class.php');
class addcateAction extends AdminAction
{
	var $Table1 = "_cate";
	var	$fieldNames =  Array('cat_id', 'cat_title', 'cat_sort', 'cat_msg' );

    function getDefaultView(&$controller, &$request, &$user)
	{
		$Table1 = PTB."".$this->Table1;
		if(empty($_POST))
			{
				foreach($this->fieldNames as $field)
					{
						$_POST[$field] = '';
					}
			}
			
			return VIEW_INPUT;
	}

    function Execute(&$controller, &$request, &$user)
	{
		$Table1 = PTB."".$this->Table1;
		$fieldInsert = "";
		$valueInsert = "";
		$arr = array();
		$i = 0;		
		$catTitle = $_POST['cat_title'];
		$catMsg = $_POST['cat_msg'];
		$arr	= array($catTitle, $catMsg);

		$fq = "INSERT INTO ".$Table1;
		$fq .= "(cat_title,cat_msg) VALUES (?,?)"; 
		$rs = $this->DB->Execute($fq, $arr);
		$controller->redirect(WEBROOT_PATH . "/".mObject."/hcontent/".mAccess."/Index");
    }    

?>

define("PTB","pp");

$Table1 = PTB."".$this->Table1;