A symbol in Lisp can have a value, also called its binding. There must be a way to distinguish the symbol itself from its value. In English these are not formally distinguished.
The President is the chief executive.
The President has a wife named Laura.
In Lisp, we denote the symbol itself by quoting it with a single-quote symbol.
(GET 'PRESIDENT 'DUTIES) (GET PRESIDENT 'SPOUSE)
Internally, the ' symbol becomes the pseudo-function QUOTE:
(GET (QUOTE PRESIDENT) (QUOTE DUTIES))Quoting a list makes a constant data structure:
(SETQ FORMULA '(= AREA (* PI (EXPT R 2))))