while(@data) works but why

[Tony Esposito]

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while(@dat = $sth->fetchrow) {
        print "@dat\n";
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This code works yet there is no 'my @dat' defined anywhere in the code.
Using Perl 5.8.x - 5.14.x

Q: Why does the variable @dat not need a 'my' in front?

Cheers!