1.verbTo take (a system, etc.) offline; to demote from an active or online state.
2.adjectiveOf a system, currently not connected (generally electrically) to a larger network. For example, a power plant which is not connected to the grid, or a computer which is not connected to the Internet or to any other communications service.
"I saved the web pages so I could read them later offline."
3.adjective(by extension) Happening in the physical world (the real world) as opposed to on the internet.
"offline dating"
4.adverbWhile offline; with an offline system.
5.adverbOutside the current meeting, in a more private setting.