Cloud Bunny has it about right. In our airline we operate the A320,
A321 and A330. Most of our Airbus pilots are 'mixed fleet' which means we fly all three variants. The A320 and A321 are considered a single type (same type rating), while the A330 is a different type. A Cross-Crew Qualification course (CCQ) qualifies A320/1 pilots to fly the A330 and the two types may then be flown together ...