Exponential, Epidemic, Endemic, and Pandemic are words we’re hearing a lot now, and they can be confusing to people without previous experience.

Here are their definitions—with an example of each.

- An
**Epidemic**is an increase in occurrences in a given area,*e.g., a lot of people getting a particular cold virus in Hackensack, New Jersey*. - A
**Pandemic**is when an Epidemic spreads throughout the world,*e.g., the Flu pandemic of 1918*. - Something being
**Endemic**means it’s a permanent feature of a group,*e.g., Chickenpox is endemic in the U.K., but Malaria is not.* - And
**Exponential**growth means that the amount of growth something experiences is related to how large it is already. So in the case of growth, the bigger it gets the faster it grows,*e.g., exponential growth of the number of people with the flu during a pandemic*.

So an epidemic is just an outbreak of instances of something, and it’s confined to a particular area. A pandemic is a world-wide epidemic. And endemic means something is now a permanent part of a population.

Exponents also become more dramatic depending on the size of the base.

Exponential is the interesting one. A lot of people believe it means that the number is multiplied by an exponent, like, 120^{3}. But what it actually means is that **the growth rate depends on the current size**.

So if you have something growing at a 15% rate, that starts as 100, the next time you measure it’ll be at 115. And if it’s growing at a 100% rate, then the next time you measure it’ll be 200. And in a very short amount of time you can have insanely large numbers.

Exponential growth can be shocking to people who’ve never seen it.

For example, how much money do you have if you start with a penny ($.01) and double it for 30 days?

It’s not some high number like $500, or even $1,000, or even $100,000. Nope…

**It’s $5,368,709**.

You can also have negative growth.

That’s why exponential growth is such a big deal. It’s not just the amount that it grows by—it’s that the previous total is then used as the new base.

## Summary

- An epidemic is a fast increase in instances in a particular area.
- A pandemic is a worldwide epidemic.
- Endemic means something is permanently part of a population.
- Exponential grown means the speed of the increase gets magnified as it becomes larger.