Anglicized form of Carolus (see Charles), or of its feminine derivative Carola. It has never been common as a boy's name, and has become even less so since its growth in popularity as a girl's name. This seems to be of relatively recent origin (not being found much before the end of the 19th century). It probably originated as a short form of Caroline.
Polish and Jewish (Ashkenazic): habitational name for someone from any of many places in Poland and adjacent parts of eastern Europe named Ostrów, named with Polish ostrów ‘island’, ‘water meadow’ (see Ostrow) or a cognate word in a related Slavic language.