quote is a special form in `C source code'.

(quote ARG)

Return the argument, without evaluating it. `(quote x)' yields `x'.
Warning: `quote' does not construct its return value, but just returns
the value that was pre-constructed by the Lisp reader (see info node
`(elisp)Printed Representation').
This means that '(a . b) is not identical to (cons 'a 'b): the former
does not cons. Quoting should be reserved for constants that will
never be modified by side-effects, unless you like self-modifying code.
See the common pitfall in info node `(elisp)Rearrangement' for an example
of unexpected results when a quoted object is modified.