What does it mean that the WHO has declared a pandemic?

On 11 March WHO declared COVID-19 a pandemic. The WHO used this declaration to call for urgent and aggressive action. They noted that this is a pandemic that can be controlled. Both China and the Republic of Korea have significantly declining outbreaks.

On 30 January, the WHO declared that COVID-19 was a Public Health Emergency of International Concern. In the last two weeks, the number of cases of COVID-19 has increased substantially and the number of affected countries has tripled (WHO).

Source: https://www.health.nsw.gov.au/Infectious/alerts/Pages/coronavirus-faqs.aspx#sec8