Wikipedia has an article, with references, which describes the term PIGS and its PIIGS and PIIGGS variations.

Italy is far more indebted that any of those 4(5(6)).

Considering that Italy is one of those 4(5(6)), I do not know what you mean.

Note also that national debt is just a single figure. It doesn't say what kind of debt it is (short term, long term), or, more importantly, where the money is borrowed from. It matters a lot whether a government is able to borrow money "internally" (that is, from its own population and banks) or abroad. The latter carries more risks. And then there are factors like trade deficit, unemployment rate, etc.