The cons is both Lisp's fundamental memory object and the name of a Lisp operator. The cons, as the memory object, is a memory construct which is able to store a pair of objects, known as the car and the cdr.
The cons operator offers a way to both create a cons object and also set the values. So, for example, the following command creates a cons object with the car field set to 1 and the cdr field set to 2:
> (cons 1 2) (1 . 2)
As the cons object can also store references to other cons objects in its car and cdr fields, the cons field is also able to be used as a basic building block for a series of data structures. So, a singly linked list could be constructed with cons objects such as:
> (cons 1 (cons 2 (cons 3 nil))) (1 2 3)
The previous car nested structure generates an equivalent singly linked list to the following:
> (list 1 2 3) (1 2 3)