The 'block' special form specifies a 'named-block' construct. The last expression in 'body' will be returned by the 'block' construct as its result unless a return or return-from is executed within 'block'. The return exit will exit the nearest (inner-most) 'block'. The return-from exit will exit the specified 'block'.
(block out ; outer BLOCK (print "outer") (block in ; inner BLOCK (print "inner") (return-from out "all done") (print "won't get here"))) ; prints "outer" ; prints "inner" ; returns "all done"
See the