What is "association list"

n. (context programming English) A data structure that associates keys with data; implimented as a list whose members are paired storage locations (cons cell), one element of which (the car) contains the key and the other element of which (the cdr) contains the keyed data.

In computer programming and particularly in Lisp, an association list, often referred to as an alist, is a linked list in which each list element (or node) comprises a key and a value. The association list is said to associate the value with the key. In order to find the value associated with a given key, a sequential search is used: each element of the list is searched in turn, starting at the head, until the key is found. Associative lists provide a simple way of implementing an associative array, but are efficient only when the number of keys is very small.