What is the X in X-mas?
1. Not directly connected to the computer (e.g., an off-line tape drive), or with connection suspended ("take the printer off-line").
Contrast background, on-line.
2. Not now or not here. "Let's take this discussion off-line." Specifically used on Usenet to suggest that a discussion be moved off a public newsgroup to e-mail.
See also off-line world.