Spread of a distribution

Spread is the width of the data, and the measure you report has to match the measure of center you reported with it. Pair the mean with the standard deviation, and pair the median with the IQR, which uses the median-excluded (TI-84) quartile rule on this site; the range is the crudest option because it depends only on the two extremes. For the values 10, 12, 14, 16, 18 the mean is 14, the range is $18 - 10 = 8$, and the sample standard deviation is $s = \sqrt{40/4} = \sqrt{10} \approx 3.16$. Two data sets can share the same center and still look nothing alike once you compare their spread.