**Z-score:** A Z-score, in the context of A/B testing and digital marketing, is a statistical measurement that describes a value's relationship to the mean (average) of a group of values. It's measured in terms of standard deviations from the mean. In simpler terms, a Z-score tells us how far away a certain value (like click rate, conversion rate, etc.) is from the average value. If the value is exactly at the mean, the Z-score is 0. This score is crucial in determining if the differences in results between variations in the A/B testing are statistically significant or not.

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