<OPTION>

a key to press in a software package to see what options are available in a particular function.

off line

two words in other limited instances, e.g., take a computer off line

offline

adj. one word   Not connected to or not installed in the computer. If a terminal, printer or other device is physically connected to the computer, but is not turned on or in ready mode, it is still considered offline.

on line

used as two words in limited instances, e.g., bring a computer on line

online

adj. one word    Available for immediate use. It typically refers to being connected to a remote service. For example, if you use the Internet, you are online when you have made the connection via modem and logged on to your Internet provider with your username and password. When you log off the service, you are offline.  A peripheral device (terminal, printer, etc.) that is turned on and connected to the computer is also online.

on-line

(adj. adv. form “on line”)  connected to or continually controlled by a computer.

over

prefix, no hyphen; e.g., overenthusiastic