I don't remember if it's mentioned specifically in the POD, but from my usage, the first option is always the name of the key it will use. This is handy when you want to use one character options or bundling. As in:

use Getopt::Long;
Getopt::Long::Configure('bundling');

my %options;
GetOptions(
  \%options,
  'LongName|L=s'
);

if ($options{LongName}) {
  # do something with $options{LongName}
}
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prog.pl --longname something
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prog.pl -L something
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kelan

Perl6 Grammar Student