Online and offline are terms used in telecommunications.
If a computer or a user is connected to the Internet, it is said to be "online". A website, for example, is online, because it is on the Internet.
If something is not online, it is said to be "offline". If a system is offline, it is in a disconnected state.
Online can also mean that something is set up correctly and ready to what it is supposed to do. For example:
This article uses material from the Wikipedia Simple English article Online and offline, which is released under the Creative Commons Attribution-ShareAlike 3.0 license ("CC BY-SA 3.0"); additional terms may apply (view authors). Content is available under CC BY-SA 4.0 unless otherwise noted. Images, videos and audio are available under their respective licenses.
®Wikipedia is a registered trademark of the Wiki Foundation, Inc. Wiki Simple English (DUHOCTRUNGQUOC.VN) is an independent company and has no affiliation with Wiki Foundation.