• perldoc -f last
• What happens when you try it?
• More looping examples in perldoc perlsyn

'last' and 'next' always break the innermost loop, so it's perfectly clear.

But it's a lot clearer to read if you use labels ( traditionally ALLCAPS ).

LINE:
while ( my $line = <$datafile> ) {
    my @fields = split ',', $line;
  FIELD:
    for my $field ( @fields ) {
        if ( foo() ) {
            next FIELD;
        } elsif ( bar() ) {
            next LINE;
        } else {
           more();
        }
    }
}
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It applies to for loops.

for (1..3) { ... }
for (@a) { ... }
for (my $i=10; $i--; ) { ... }
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It applies to while and until loops.

while (f()) { ... }
until (f()) { ... }
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It applies to bare loops.

{ ... }
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It does NOT apply to conditional statements.

if (f()) { ... }
unless (f()) { ... }
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It does NOT apply to statement modifiers.

... while f();    Including: do { ... } while f();
... for @a;
... if f();
etc
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It does NOT apply loop-like functions.

grep { ... } @a
map { ... } @a
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Please see T.I.T.S. - it's faster even than asking PerlMonks! (And, bonus, sounds at least slightly illicit!)