1A statistical procedure for identifying changes in the probability distribution of a given process by considering cumulative sums associated with that process; a cumulative sum used in this procedure. Usually attributive, as "cusum chart", "cusum test", etc.
2A method for analysing the authorship of texts by considering cumulative sums which chart the frequencies of a particular stylistic feature (especially sentence length) throughout a given text.
1960s; earliest use found in Quality Control & Applied Statistics. Acronym from the initial letters of cumulative sum.