The best definition of an outlier among the options provided is:
Definition #2: a value that skews results because it is much higher or lower than the other data.
This definition accurately captures the essence of what an outlier is: a data point that significantly differs from the other observations in a dataset, which can affect statistical analyses and results.
Definitions #1 and #3 do not accurately define an outlier. Definition #1 focuses on a "number of suitable data points," which isn't relevant to the concept of outliers. Definition #3 assumes that outliers are always inaccurately calculated, which is not necessarily true; outliers can be legitimate observations that are simply extreme values.