The difference can be observed by running the following two snippets.

use strict;
my @array = (1, 2, 3);
my $item = 'z';
foreach $item (@array) {}
print($item);  # Prints 'z' (not '3'!!!).
[download]

use strict;
my @array = (1, 2, 3);
foreach my $item (@array) {}
print($item);  # Compile error. $item only in scope for loop.
[download]