What's the difference between a pandemic and an epidemic?

[WibblyPigRocks]

Or are they the same thing? Is a pandemic a certain sort of epidemic?

I can't seem to find a straight answer anywhere and was just interested.

an epidemic when a virus is widespread (with a predefined threshold) in a country. A pandemic has a specific WHO definition but in general terms it means a virus that is becoming (or has become) an epidemic in countries world wide.

doesn't the 'pan' prefix mean worldwide? that's what I thought.