ELI5: Explain Like I'm 5

Series (mathematics)

Series (mathematics) is a way of adding up numbers. It's like when you're trying to figure out how much all of the things in your shopping cart cost. You can take all of the prices of the items and add them up. With a series, you can do the same thing, but with an infinite number of items. Instead of adding up all the prices, you can add up all the numbers in the series. The series is like a shopping cart, but with an unlimited number of items to add.