VdT – Vino da Tavola – This is the lowest and least regulated class of wine. Because it is less restricted by government regulation, the wine maker is free to create it as he or she wishes. Most are adequate, affordable and generally appropriate for casual dinner wine. Because they can vary so much, there are some that are quite good.
DOC – Denominazione di Origine Controllata – The name means ‘designation of origin controlled’. This requires that a wine (or food) product must come from the region indicated on the label. You can find a list of Italian DOC wines on Wikipedia at this link.
DOCG – Denominazione di Origine Controllata e Garantita – Literally ‘designation of origin controlled and guaranteed’, this standard is enforced by government regulators who test and taste the wine to ensure compliance. Not a bad job if you can get one. Currently, there are 47 DOCG wines, and here is a list on Wikipedia.