The word 'PANDEMIC' is a one word substitution for :

A disease that spreads over a whole country or the whole world.

The word 'PANDEMIC' is a one-word substitution for: A disease that spreads over a whole country or the whole world.

A riot outbreak after a football match. This is not related to a pandemic. A more appropriate term for a riot outbreak after a football match might be "hooliganism" or "post-match violence."

A disease that spreads over a whole country or the whole world. This is correct. A pandemic is a global outbreak of a disease affecting a large number of people across countries or continents. 

An event organized by 'Pandal' association. This is not related to a pandemic. An event organized by a 'Pandal' association might be associated with festivals, gatherings, or celebrations, but it is not the definition of a pandemic. A spiritual gathering. This is not related to a pandemic.

A spiritual gathering might be referred to as a "congregation" or "spiritual assembly," but it is not the definition of a pandemic, which specifically relates to the widespread occurrence of a disease.