A cumulative distribution is a means of representing the variation of some attribute by giving running totals of the resource with attribute values less than or equal to a specified series of values.

For example, a cumulative areal distribution of lakes would give, for any value a of area, the total area covered by lakes with individual area less than or equal to alpha. A cumulative frequency distribution for lake area would give the total number of lakes with area less than or equal to alpha. The cumulative distribution function (cdf) of some specified attribute of a population is the function F(x) that gives the proportion of the population with value of the attribute less than or equal to x, for any choice of x. For example, if the attribute was lake area in hectares, F(a) would give the proportion of lakes with area less than or equal to a ha. (In some cases, the word "cumulative" may be omitted in discussions of the cdf, and the cdf is called the distribution function.)