Defining a "cadillac" healthcare plan

Okay, so I found several articles that seem to explain what the government calls a "cadillac" employer-paid healthcare plan:

• What Makes a Health Plan a 'Cadillac'? (10.1.09) – by Keith B. Richburg, WashingtonPost.com
• Do I have a "Cadillac Plan"? (10.14.09) – by Christopher Beem, Slate.com
• 'Cadillac Care' is largely a myth (12.18.09) - by Allan Sloan, WashingtonPost.com
• Serafini clarifies reference to 'Cadillac' health care plan (1.21.10) - by Erin Julius, Herald-Mail