EVAL function interprets (or compiles and runs) the argument and returns the result. See also APPLY, LAMBDA, FUNCALL.

(eval '(+ 1 2)) => 3
(eval '(let ((x 2)) (sin x))) => 0.9092974
(let ((expr '(((x 2)) (sin x)))) (eval (cons 'let expr))) => 0.9092974