package main;
my $var=6;
sub foo {
        our $var;
        $var=5;
}

print $var;
foo();
print $main::var;
print $var;
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What is means is, that within the subroutine foo, I can get to the package $var without having to use a full package name ($main::var). The our declaration makes it clear that within this lexical scope "$var" means the package variable, not the lexical $var that exists in the enclosing scope.

Sometimes there are uses for "our" inside of subroutines.

update: of course I meant $main::var