Capturing preserves a variable beyond the end of its normal scope.

sub make_closure {
   my ($x) = @_;
   return sub { $x };
}

my $c1 = make_closure("a");
my $c2 = make_closure("b");

say $c1->();  # a
say $c2->();  # b
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The $x from the first call to make_closure and the $x from the second call to make_closure are kept alive beyond the end of their normal scope (the end of that call to make_closure).