Simplified Common Lisp reference
Symbol class: Mathematics, Arithmetics, Logic and Comparisons
Symbol type: macro
orforms(zero or more) => value
Argument description:
forms forms which value is considered

OR macro computes logical "or" function. Forms evaluation starts from left. Value from the first form that decides result is returned so forms at end of argument list may not evaluated.

(or t t t nil t) => T
(or nil nil nil) => NIL
(or) => NIL
(or (progn (write "SEEN") 123) (progn (write "UNSEEN") t)) => "SEEN" 123
(or 4 5 6) => 4
Function indexFull documentation for or (HyperSpec)