Oh, I only minored in math, I’m no expert either! Yeah, your explanation was really fine, I just thought the “sum of a geometric series” thing might ring a bell for some readers.

Yeah, that’s basically how I remember it, though it’s not always stats–the terms are used in other fields of math as well. A first calculus class typically includes a proof that the limit of the sum of an infinite geometric series (a + ar + ar^2 + ar^3 + …) tends towards a/(1-r) where a is the first term and r is the ratio of successive terms, provided that -1 < r < 1. (Otherwise the series diverges and the limit isn’t defined.)