Partial sums are another way to think of finite series. Why partial? Because they are a part of an infinite series! Thinking of the partial sums of an infinite series helps us analyze the infinite series itself.
This might seem unbelievable at first, but for a certain class of geometric sequences, we can take the sum of all the infinite terms in the sequence and end up with a finite number! This sum is called an infinite geometric series. Learn when and how it can be found.