What is a pandemic? What about the Influenza virus contributes to its ability to create a pandemic ...

A pandemic is a rapidly spreading, highly infectious, potentially dangerous pathogen.

There are two reasons the flu virus can cause pandemics.
1. the RNA polymerase lacks a proof-reading ability therefore mutations accumulate in the RNA genome at an accelerated rate.

2. The virus is strange in that it has a segmented genome (much like we have chromosomes). It has 8 segments and when the viruses are built the segments stuffed into the virion are random.

This becomes a major problem if the cell is infected with influenza from 2 different sources for example human flu and bird flu. The potential here is that a human flu ends up with genes from the bird flu which would cause major changes to the virus and the immune system would be baffled.