An anonymous subroutine is a reference to a subroutine. For lots of infor: perlref.

For the quick rundown:
Sub routines can be referenced, and then later dereferenced for access. Useful if you need to create an option handler or something:

$opt = "opt" . $ARGV[0];

$subhash = {
    opt1 => sub { print "This is option one"; },
    opt2 => sub { print "This is options two"; }
};

# indicate a function when dereferencing with &
&{$subhash->{$opt}};
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