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.
German (Grüber) and Jewish (Ashkenazic): topographic name for someone who lived in a depression or hollow, from (respectively) Middle High German gruobe, German Grube ‘pit’, ‘hollow’ + the suffix -er denoting an inhabitant. As a Jewish name it can also be one of names randomly distributed by government officials.