What is a pandemic anyway?

In Is This a Pandemic? Define 'Pandemic' in the New York Times, Dr. Lawrence Altman begins:

After decades of warnings about the inevitability of another pandemic of influenza, it is astonishing that health officials have failed to make clear to the public, even to many colleagues, what they mean by the word pandemic.

Count me among those who are confused about the difference between a pandemic and an epidemic. I assumed that after reading the rather lengthy article I would understand the distinction. But no, the whole article is about the fact that it's confusing and no one's defined the terms.It would have been helpful if Altman had at least floated a couple of competing definitions. The  closest he comes is a quote in the last column from Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. He says,

A pandemic is basically a new or novel agent emerging with worldwide transmission.

That's why the seasonal flu isn't a pandemic --even though it spreads around the world.Do a Google or Bing search on "pandemic versus epidemic" and you'll come up with answers that essentially say a pandemic is a big epidemic. Not everyone agrees with Osterholm that a pandemic has to be a novel agent.Maybe we should stop using the term pandemic for a while.