What Is A Pandemic?

Pandemics are states of dis­ease that sharply increase in pop­u­la­tions around the world with infec­tions tak­ing place more or less simul­ta­ne­ous­ly.
While it usu­al­ly refers to infec­tious dis­eases, such as plague or influen­za, it is often used to refer to oth­er health con­di­tions includ­ing can­cer, obe­si­ty, and even addic­tion.
Pathogen trans­mis­sion through a pop­u­la­tion is typ­i­cal­ly cov­ered by five gen­er­al descrip­tions. 
An endem­ic infec­tion is one that remains rel­a­tive­ly sta­ble over time, infect­ing an expect­ed num­ber of hosts in ways that are usu­al­ly fair­ly well under­stood. The par­a­site schis­to­so­mi­a­sis, for exam­ple, can cause seri­ous infec­tions, but is usu­al­ly con­tained with­in trop­i­cal regions in num­bers that don’t vary much from year to year.

An out­break describes a sud­den spike in trans­mis­sions in a local­ized region. For exam­ple, in 2019 the Democratic Republic of the Congo saw a steep rise in peo­ple con­tract­ing the Ebola virus in the nation’s east. While the World Health Organisation (WHO) viewed it as a pub­lic health emer­gency, its con­tain­ment meant it was­n’t an epi­dem­ic.
Widespread out­breaks across wider regions tend to be regard­ed as epi­demics. The spread of Ebola across Western Africa between 2013 and 2016 is often described using the word epi­dem­ic.
Once the epi­dem­ic has proven to be capa­ble of mov­ing around the world in a way that sus­tains wide­spread, ongo­ing infec­tions, it can be regard­ed as a pan­dem­ic. 

When does an epidemic officially become a pandemic?

In 2009, a new kind of influen­za A virus known as H1N1 emerged in an out­break in the United States. It quick­ly spread, and was defined by the WHO as a pan­dem­ic based on a for­mal process that took into account the pre­cise nature of the coun­tries where an infec­tion was diag­nosed. 
As infec­tions from the 2019-coV coro­n­avirus con­tin­ued to spread in ear­ly 2020, the WHO declared that they no longer use a for­mal clas­si­fi­ca­tion to des­ig­nate when an epi­dem­ic becomes a pan­dem­ic.
Concerned pre­ma­ture use of the term could cause pan­ic, offi­cials instead described the glob­al epi­dem­ic as hav­ing “pan­dem­ic poten­tial”, while claim­ing that they weren’t yet observ­ing the “uncon­tained glob­al spread” of the virus. From (sci​enceal​ert​.com)