The terms online and offline (also on-line and off-line) have specific meanings with respect to computer technology and telecommunication.The concepts have however been extended from their computing and telecommunication meanings into the area of human interaction and conversation,such that even offline can be used in contrast to the common usage of online (e.g.,"I bought that shirt offline").
In computer technology and telecommunication,online and offline are defined by Federal Standard 1037C.They are states or conditions of a "device or equipment" or of "a functional unit".To be considered online,one of the following must apply to a device:
Under the direct control of another device
Under the direct control of the system with which it is associated
Available for immediate use on demand by the system without human intervention
Connected to a system,and is in operation
Functional and ready for service
In contrast,a device that is offline meets none of these criteria (e.g.,its main power source is disconnected or turned off,or it is off-power).
One example of a common use of these concepts is a Mail User Agent that can be instructed to be in either online or offline states.One such MUA is Microsoft Outlook.When online it will attempt to connect to mail servers (to check for new mail at regular intervals,for example),and when off-line it will not attempt to make any such connection.The online or offline state of the MUA does not necessarily reflect the connection status between the computer on which it is running and Internet.That is,the computer itself may be online—connected to Internet via a cable modem or other means—while Outlook is kept offline by the user,so that it makes no attempt to send or to receive messages.Similarly,a computer may be configured to employ a dial-up connection on demand (as when an application such as Outlook attempts to make connection to a server),but the user may not wish for Outlook to trigger that call whenever it is configured to check for mail.