In Lisp, car, cdr, and cons are fundamental functions. The cons function is used to construct lists, and the car and cdr functions are used to take them apart.
The cons function constructs lists; it is the inverse of car and cdr. For example, cons can be used to make a four element list from the three element list, (fir oak maple):
(cons 'pine '(fir oak maple))
After evaluating this list, you will see
(pine fir oak maple)
The cdr of a list is the rest of the list, that is, the cdr function returns the part of the list that follows the first item. Thus, while the car of the list '(rose violet daisy buttercup) is rose, the rest of the list, the value returned by the cdr function, is (violet daisy buttercup).
You can see this by evaluating the following in the usual way:
(cdr '(rose violet daisy buttercup))
When you evaluate this, (violet daisy buttercup) will appear in the echo area.
Source: http://www.rattlesnake.com/intro
