Typical distance from the mean. The exam never asks you to compute it — the formula is not on the reference sheet; it asks you to COMPARE two sets: more spread out from the center means larger SD. It has nothing to do with the mean's value: 10,10,10,10,10 and 8,9,10,11,12 share a mean of 10 but have SD 0 and ≈ 1.41.