performs a short-circuiting or
Evaluates the forms from left to right. As soon as one evaluates to a truthy value, will return that value. Otherwise it will proceed to evaluating the next form.
(or (+ 1 2 3) false "not returned")
Will return 6, never evaluating
false (false) and
"not returned", whereas:
(or false '() "returned")
Will return the string “returned”.