Spread measured as average squared distance from the mean. Standard deviation is the square root — same units as the data. Toggle the squares on to see why it's "squared".
Mean (μ)—
Variance (σ²)—
Std Dev (σ)—
12
Why squared? Plain deviations sum to zero (positives cancel negatives). Squaring makes everything positive — and it penalizes big errors more than small ones. The √ at the end just brings us back to the original units.