Simplified Common Lisp reference
Symbol class: Sequences (Lists, Strings) and Arrays
Symbol type: function
copy-seqseq => sequence
Argument description:
seq a sequence

COPY-SEQ function makes new sequence copy from old sequence. Note that there is no COPY-ARRAY function, but it can be emulated by this tricky code bellow:

(defun copy-array (array)
 (let ((dims (array-dimensions array)))
    (make-array dims :displaced-to array)
(let ((a "hello world")) (eq a (copy-seq a))) => NIL
(let ((a "hello world")) (equal a (copy-seq a))) => T
Function indexFull documentation for copy-seq (HyperSpec)