As a girl's name this is a pet form of Jacqueline, as in the case of Jackie Kennedy Onassis (1929–94). It was originally a boy's name, a pet form of Jack. The racing driver Jackie Stewart (b. 1939) was originally named John Young Stewart.
Portuguese and Galician: habitational name from any of various places named Medeiros, from Portuguese and Galician medeiro ‘place where shocks of maize are gathered’ (a derivative of meda ‘shock’, ‘stack’, Latin meta ‘(pyramidshaped) post’).