Turned on and connected. For example, printers are online when they are ready to receive data from the computer. You can also turn a printer offline. While the printer is offline, you can perform certain tasks such as advancing the paper, but you cannot send data to it. Most printers have an online button you can press to turn the machine on- or offline.
Users are considered online when they are connected to a computer service through a modem. That is, they are actually on the line.
The term also is spelled as on-line. Also see Internet Grammar Concerns in the Did You Know . . . ?section of Webopedia.
