>>When a form on a web-site says CC (Credit Card) I can always pay with my debit card.

Here in Canada, many debit/bank cards now have affiliation with Visa or Mastercard (obvious with a logo in corner), and CAN be used as Credit Cards.

But that hasn't been the case historically - debit/bank card would work on bank's ATM and related Interact/Plus systems. But until semi-recently would NOT work if you accidentally hit "Credit" instead of "Debit" on ATM or retailer's POS system, and would NOT work on websites requiring Credit card - completely different paths. And to my knowledge many bank/debit cards in Canada still cannot serve as credit cards - they just don't have that capability/afiliation baked in.

Note - I speak as a semi-observant customer, I have no systems-based knowledge of these things :-)