In computer programming, cdr (pronounced cudder) and car are a pair of primitive functions in Lisp and its best known offspring, Scheme.
car are used to refer to the tail (
cdr) and head (
car) of a list:
(cdr '(A B C))yields
(car '(A B C))yields
car(Contents of Address Register) and
cdr(Contents of Decrement Register).
Portions from NILS' LISP PAGES - http://t3x.dyndns.org/LISP/QA/carcdr.html