in reference to computers, "directly connected to a peripheral device," 1950 (originally as on-line).
online in Science
online
(ŏn'līn') Connected to or accessible by means of a computer or computer network.
online in Culture
online definition
A term referring to locations on or use of the Internet. The term can be used to refer to a specific location or Web page (“Our sales catalogues can be found online at — ”) or to a personal activity (“I went online to find the information you wanted.”)