Seán Crowe (Dublin South West, Sinn Fein) | Oireachtas source

This may seem like a silly question, but what signifies that a disease is a rare disease? For example, I presume the coronavirus, when it started off, at one stage would have been seen as a rare disease but it became a pandemic. Would long Covid, for instance, fit in with the category of rare disease, even though the figures per head of population would suggest its prevalence is quite high?