Central Limit Theorem: A sampling distribution of the mean is approximately normally distributed if the sample size is sufficiently large. This is true no matter what the population distribution is.

This visualization was adapted from Kristoffer Magnusson's fantastic visualization of confidence intervals. Another visualization of confidence intervals for a mean: Interactive Applet: Confidence ...

Technical Terms Approximate Query Processing (AQP): A technique for retrieving near-exact query results from large datasets using data summarisation and sampling methods.