**Confidence interval: **A confidence interval is a range of values, derived from a statistical calculation, that is likely to contain an unknown population parameter. In marketing, it is often used in A/B testing to determine if the variation of a test actually improves the result. The confidence interval gives us a defined range where we expect the true value to fall, based on our desired confidence level. If the interval is wide, it means our results may not be very reliable, whereas a narrow interval indicates a higher level of accuracy.