The word comes pandemic comes from ancient Greek — pan (meaning "all") and demos (meaning people), or simply put — all the people.  Of course, people across the globe suffer from the seasonal flu, and many die from it. But it isn't considered a pandemic because it is generally harmless to the healthy.

The difference between epidemic and pandemic are as follows: an epidemic is a disease outbreak that is rapidly spreading in a limited region.  A pandemic is an epidemic that is actively spreading to multiple regions across the globe. 

According to the Oxford English Dictionary (OED), the word "pandemic" was first used in English in the mid-1600s.  Specifically, the OED's earliest evidence for the word "pandemic" is from 1659 in the writings of J. Rogers. At this time, the word was primarily used as an adjective, often in a general sense meaning "universal" or "widespread".   The noun form of "pandemic," referring to "a pandemic disease; an outbreak of such a disease," is recorded by 1832. 

Examples of pandemic used in a sentence:  
"Companies should prepare for a pandemic flu the way they would for a blizzard." 
"The idea that this flu could reach pandemic proportions is a chilling thought." 
"Experts warned of the impending threat of a global pandemic if the virus was not contained. 
"They feared a new cholera pandemic." 
"Even in the East plague was confined to more or less clearly localized epidemics; it showed no power of pandemic diffusion." 
"In short, if we regard the history of this disease as a whole, it appears to have lost such power from the time of the Great Plague of London in 1665, which was part of a pandemic wave, until the present day."

Just the facts:

PANDEMIC Definition & Meaning - Merriam-Webster