Vivify:to give life to; bring to life; to animate.

my $hash;
print "\$hash is: ", defined $hash ? $hash : "undefined", "\n";
if ($hash->{one}){
    print "'one' exists\n";
}
print "\$hash is: ", defined $hash ? $hash : "undefined", "\n";
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$hash is undefined, but when we use it as if it were a reference to a hash ($hash->{one}) perl automatically brings a hash reference to life and stores it in $hash. Hence, it autovivifies the hash reference for us.