Usual definition of epidemic is just significant spread of decease - usually at least 5% of local (country, state, city) population, but most of them time it is much higher (flu epidemic can be declared with 11-15% and more).
Pandemic is just same thing, but if we have different countries effected at same time.
If you note WHO texts that declared coronavirus pandemic with special notices that it is not actually pandemic, but we make it such to force more strong measures taken.
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