Depends on how you define it. The text is talking about global variables, which are available to code outside their containing block:
$i = 3;
Prints 3. Compare with:
my $i = 3;
Without strict, this prints only a newline. This code declares a lexically scoped $i, which only persists through the end of its enclosing block. One of the best things about strict/warnings is that perl will complain about this kind of thing, possibly saving you a bunch of time hunting down a confusing error in a large program.