This is called Heredoc syntax, and allows you to define long strings, without having to care about escaping double-quotes (nor single, btw)
Syntax goes like this :
$str = <<<EOD
Example of string
spanning multiple lines
using heredoc syntax.
EOD;
Note this (quoting the doc) :
A third way to delimit strings is the
heredoc syntax: <<<. After this
operator, an identifier is provided,
then a newline. The string itself
follows, and then the same identifier
again to close the quotation.
The closing identifier must begin in
the first column of the line. Also,
the identifier must follow the same
naming rules as any other label in
PHP: it must contain only alphanumeric
characters and underscores, and must
start with a non-digit character or
underscore.
And also note it is not exactly the same as nowdoc syntax, which only exists since PHP >= 5.3