A probability distribution is an input model: a description of the variation a simulation draws from. This page holds the common ones, grouped here by the modeling question each answers. Open a tile to see its shape change with its parameters, how it relates to the others, and how a random variate is generated from it.
Four families, each a small tree rooted at the distribution the rest are built from. Every box is a link to that distribution's tab; a solid arrow derives one distribution from another, and a dashed arrow marks a special case, either landing in a different family, shown lower down, or closing a loop back onto a root already drawn.