It means that a hash reference is being de-referenced:

>perl -wMstrict -le
"my $frm = { foo => 11,  bar => 22 };
 print $$frm  {bar};
 print $frm ->{bar};
"
22
22
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The preferred operator for de-referencing is the  -> (arrow) operator.

See perlref, perlreftut.