ANSI Common Lisp 1 Introduction 1.4 Definitions 1.4.1 Notational Conventions
220.127.116.11 Nonsense Words
When a word having no pre-attached semantics is required (e.g., in an example), it is common in the Lisp community to use one of the words "foo," "bar," "baz," and "quux." For example, in
(defun foo (x) (+ x 1))the use of the name foo is just a shorthand way of saying "please substitute your favorite name here."
These nonsense words have gained such prevalance of usage, that it is commonplace for newcomers to the community to begin to wonder if there is an attached semantics which they are overlooking - there is not.