Like the title says!

One concrete example is geometric series (but only when each term is some fraction of the previous).

Here’s the formula that dictates the resultant finite sum:

• $a$ is known as your “starting” amount
• $r$ is the “multiple” (remember, in a geometric series, each term is some “multiple” of the previous term)
• $r$ must be less than 1 in order for this sum to be finite (i.e. this formula assumes r less than 1!)
• so not all geometric series result in a finite sum, only ones with $r$ less than one

That’s kinda cool!