The terms online and offline (also on-line and off-line) have specific meanings with respect to computer technology and telecommunication. In general, "online" indicates a state of connectivity, while "offline" indicates a disconnected state. In common usage, "online" often refers to the Internet or the World Wide Web.

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 those Marcus Fenix figurines offline"). Another usage runs contrary to the expected meaning: 'offline' as "from an online source", e.g. "I bought my textbook from Amazon" = "I got it offline".

Standard definitions

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).