Available for immediate use. It refers to being connected to the Internet or any remote service where there is no delay in accessing the network. For example, with cable modem and DSL service, you are online all the time. On the other hand, when you connect via a dial-up analog modem, you are online after you dial in and log in to your Internet provider. When you log out, you are "offline."
Peripherals Are Also Online
A peripheral device (terminal, printer, etc.) that is turned on and connected to the computer is also online. For example, if your data are on a disk attached to your computer, the disk and the data are said to be online. If your data are on a removable disk cartridge in your desk drawer, it is offline. A printer can be taken offline by simply pressing the ONLINE, GO or SEL button. The printer is still attached and connected, but is internally cut off from receiving data from the computer. Pressing the button turns it back online.
Online vs. Batch
In the 1960s and 1970s, the ancient days of computers, systems were designed as either online or batch. Online meant terminals were connected to a central computer, and batch meant entering batches of transactions (from punch cards or tape) on a second or third shift. The term "transaction processing" evolved from online processing. See transaction processing
. See also nearline
Want to Impress Your Friends?
Although truly overkill, it is not incorrect to say that you work with "online, real-time, transaction processing systems" (every major company has one or more). In today's age of buzzwords, this phrase still sounds pretty high tech. But if you say this at your next cocktail party, be careful. Your friends will start asking you how to get their computers to work better, but an experienced computer professional will probably just chuckle.